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1.
New sulfur derivatives of phosphoramidite ligands were synthesized and the impact of the sulfur unit on the spectroscopic properties of their rhodium and iridium complexes was investigated. The new ligands Bn 2NPSCH 2CH 2S a( P- Sa) (Bn = benzyl, 4), Bn 2NPSCHCHS a(CH 2) 3C aH 2( P- Sa)( Ca- Sa) ( 6) and Bn 2NP(4-XC 6H 4OMe) 2 (X = S, 7a; X = O, 7b) were converted to the rhodium and iridium complexes trans-[Rh(CO)Cl(L) 2] (L = 4, 6, 7), [RhCl(COD)(L)] (L = 4, 6, 7), [IrCl(COD)( 7a)] and [IrCl 2Cp∗( 6)]. For comparison, some phosphoramidite complexes of these formulations also were synthesized. The new metal complexes were spectroscopically analyzed. For the carbonyl complexes, the νCO IR stretching frequencies were lower than for the corresponding phosphite and phosphoramidite ligands. The 1JPRh coupling constants for the rhodium complexes with the new ligands were also smaller than for the respective phosphoramidite and phosphite complexes. Finally, the 1JPSe coupling constants of the selenides of the new ligands were lower than those of the phosphoramidite ligands but higher than for PPh 3. The spectroscopic data reveal that the new thio ligands 4, 6 and 7a are more electron donating than phosphites and phosphoramidites but less electron donating than PPh 3. 相似文献
2.
K + and Na + fluxes and ion content have been studied in roots of Atriplex nummularia Lindl. and Avena sativa L. cv Goodfield grown in 3 millimolar K + with or without 3 or 50 millimolar NaCl. Compartmental analysis was carried out with entire root systems under steady-state conditions. Increasing ambient Na+ concentrations from 0 to 50 millimolar altered K+, in Atriplex, as follows: slightly decreased the cytoplasmic content (Qc), the vacuolar content (Qv), and the plasma membrane influx and efflux. Xylem transport for K+ decreased by 63% in Atriplex. For oat roots, similar increases in Na+ altered K+ parameters as follows: plasma membrane influx and efflux decreased by about 80%. Qc decreased by 65%, and xylem transport decreased by 91%. No change, however, was observed in Qv for K+. Increasing ambient Na+ resulted in higher (3 to 5-fold) Na+ fluxes across the plasma membrane and in Qc of both species. In Atriplex, Na+ fluxes across the tonoplast and Qv increased as external Na+ was increased. In oat, however, no significant change was observed in Na+ flux across the tonoplast or in Qv as external Na+ was increased. In oat roots, Na+ reduced K+ uptake markedly; in Atriplex, this was not as pronounced. However, even at high Na+ levels, the influx transport system at the plasma membrane of both species preferred K+ over Na+. Based upon the Ussing-Teorell equation, it was concluded that active inward transport of K+ occurred across the plasma membrane, and passive movement of K+ occurred across the tonoplast in both species. Na+, in oat roots, was actively pumped out of the cytoplasm to the exterior, whereas, in Atriplex, Na+ was passively distributed between the free space, cytoplasm, and vacuole. 相似文献
3.
The ability of partially purified human and guinea-pig haematogenous cell populations, when cultured in vitro, to metabolise arachidonic acid (AA) has been studied. Supernatants from 24 hour cell culture have been subjected to analysis for products of AA metabolism by gas chromatography with electron-capture detection.The cell types studied were human peripheral blood monocytes (both glass adherent and non-adherent), neutrophils, eosinophils and leukemic leucocytes; thoracic duct lymphocytes and lung alveolar macrophages. From the guinea-pig, induced and non-induced macrophage or neutrophil enriched peritoneal exudate populations, lymph node cells, peritoneal eosinophils and peripheral blood platelets were examined. Supernatants were assayed for the presence of PGE 2, PGD 2, PGF 2α, TXB 2 and 6-keto-PGF 1α. In all types studied PGE 2 and TXB 2 were the major products formed. The identification of PGE 2 and TXB 2 was confirmed by GC/MS with multiple ion monitoring.The results have been compared with other reports and their possible significance discussed in relation to the proposed role of prostaglandins as mediators and modulators in immunopathology. 相似文献
4.
A new series of antibacterial and antifungal triazine-derived mono- and di-substituted (symmetrical and unsymmetrical) Schiff-bases and their cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments and IR and electronic spectral measurements. IR spectra indicated the ligands to act as tridentate towards divalent metal ions via a trazine-N, the azomethine-N and, indole-NH and deprotonated-O of salicylaldehyde. The magnetic moments and electronic spectral data suggest octahedral geometry for the Co(II), Ni(II) and Zn(II)complexes and square-pyramid for Cu(II) complexes. NMR spectral data of the ligands and their diamagnetic zinc(II) complexes well-define their proposed structures/geometries. Elemental analyses data of the ligands and metal complexes agree with their proposed structures/geometries. The synthesized ligands, along with their metal complexes were screened for their antibacterial activity against Escherichia coli, Bacillus subtillis, Shigella flexneri, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella typhi and for antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata. The results of these studies show the metal complexes to be more antibacterial/antifungal against two or more species as compared to the uncomplexed Schiff-base ligands. 相似文献
5.
Summary Intermolecular transposition of Tn 2660 into pCR1 was measured at 30°C in recA
– and recA
+ hosts as between 2.6 and 5.5x10 –3, a similar value to that previously found for Tn 3. No cointegrate structures were found under conditions where 10 4 transposition events occurred. Immunity to intermolecular transposition of Tn 2660, similar to that found for Tn 3 was demonstrated by showing that the above transposition frequency was reduced by a factor of between 10 –3 and 10 –4 when a mutant Tn 2660 (resulting in the synthesis of a temperaturesensitive -lactamase) was present in the recipient plasmid. Intramolecular transposition of Tn 3 was found to occur under the same conditions as previously demonstrated for Tn 2660 giving rise to similar end products, in which the newly introduced Tn 3 is oriented inversely to the resident Tn 3 and the DNA sequence between the two transposons has been inverted. Thus, in all respects functional identity of the transposition activities of Tn 3 and Tn 2660 is shown, thereby identifying characteristics of intramolecular transposition that are not readily accommodated by current models of transposition. 相似文献
6.
NMR and FT-IR Studies of the conformational changes of guanosine and guanosine-5′-monophosphate upon substitution of the H8 of guanine by a heavy, large atom, such as bromine, are presented. The conformational forms, syn, anti, C2′- endo and C3′- endo and gg, gt and tg rotamers of the above molecules are compared to those of their metal (Mg 2+ and P t2+) adducts, where the metal is fixed to the N7 nitrogen atom of guanine. The antitumor activity of cisplatin is discussed with relation to the conformational form and the effect of cisplatin is compared to the effects of the Mg 2+ ion and carcinogens. 相似文献
7.
N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k
cat/ K
m) varied from 1 ×10 7 M −1 s −1to 2.6×10 8 M −1 s −1 at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable
groups with p K
a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed
that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were
consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent
bimolecular rate constants varied from 1.8×10 5 M −1 s −1 to 2.0×10 7 M −1 s −1 at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent
bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed
in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO,
fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×10 8 M −1 s −1 and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×10 7 M −1 s −1 and 0.29 eV.
Received: 20 September 1999 / Accepted: 24 February 2000 相似文献
8.
We examined the embryological development of anthers and ovules from Astraea ( A. lobata and A. praetervisa) and Croton ( C. floribundus, C. fuscescens, C. glandulosus, C. lundianus, C. piptocalyx, C. urucurana and C. triqueter) focusing on features with systematic significance for the group. Some of these features are common in Euphorbiaceae including: a dicotyledonous type of anther wall formation, a secretory tapetum, a mixed origin of the outer ovule integument, an epidermal origin of the inner ovule integument, the occurrence of many archesporial cells inside the ovules and a megagametophyte of the Polygonum‐type. Other features, such as the presence of styloid crystals in the tapetum, an idioblast with a druse in the endothecium, simultaneous and successive microsporogenesis, and a functional micropylar megaspore, have not previously been reported in the family. These characters appear to distinguish Croton and Astraea from other Euphorbiaceae and possibly represents autapomorphies for the tribe Crotoneae. 相似文献
9.
During knee movement, femoral cartilage articulates against cartilage from the tibial plateau, and the resulting mechanical behavior is yet to be fully characterized. The objectives of this study were to determine (1) the overall and depth-varying axial and shear strains and (2) the associated moduli, of femoral and tibial cartilages during the compression and shearing of apposing tibial and femoral samples. Osteochondral blocks from human femoral condyles (FCs) characterized as normal and donor-matched lateral tibial plateau (TP) were apposed, compressed 13%, and subjected to relative lateral motion. When surfaces began to slide, axial (? Ezz) and shear ( Exz) strains and compressive ( E) and shear ( G) moduli, overall and as a function of depth, were determined for femoral and tibial cartilages. Tibial ? Ezz was ~2-fold greater than FC ? Ezz near the surface (0.38 versus 0.22) and overall (0.16 versus 0.07). Near the surface, Exz of TP was 8-fold higher than that of FC (0.41 versus 0.05), while overall Exz was 4-fold higher (0.09 versus 0.02). For TP and FC, ? Ezz and Exz were greatest near the surface and decreased monotonically with depth. E for FC was 1.7-fold greater than TP, both near the surface (0.40 versus 0.24 MPa) and overall (0.76 versus 0.47 MPa). Similarly, G was 7-fold greater for FC (0.22 MPa) than TP near the surface (0.03 MPa) and 3-fold higher for FC (0.38 MPa) than TP (0.13 MPa) overall. These results indicate that tibial cartilage deforms and strains more axially and in shear than the apposing femoral cartilage during tibial–femoral articulation, reflecting their respective moduli. 相似文献
10.
Objectives were to determine the effects of advancing gestation, maternal nutrient restriction during early and mid-gestation, and realimentation on fetal liver and jejunal mass and energy use in both dams and fetuses. On day 30 of pregnancy, multiparous, non-lactating beef cows (initial BW=621±11.3 kg and body condition score=5.1±0.1) were assigned to one of the two dietary treatments: control (CON; 100% requirements; n=18) and restricted (R; 60% requirements; n=28). On day 85, cows were slaughtered (CON, n=6; R, n=6), and remaining cows continued on control (CC; n=12) and restricted (RR; n=12) diets, or were realimented to the control diet (RC; n=11). On day 140, cows were slaughtered (CC, n=6; RR, n=6; RC, n=5), remaining cows continued on the control diet (CCC, n=6; RCC, n=5), or were realimented to the control diet (RRC, n=6). On day 254, all remaining cows were slaughtered. Maternal liver O 2 consumption linearly increased ( P⩽0.04) and jejunal weight (g/kg) linearly decreased ( P=0.04) as gestation advanced in CON groups. Fetal BW, and hepatic and small intestinal absolute mass, protein content and O 2 consumption linearly increased ( P⩽0.04) as pregnancy advanced in CON groups. However, mass and O 2 consumption relative to BW linearly decreased ( P⩽0.001) in the fetal liver in CON groups. When analyzing the effects of dietary treatment, at day 85, fetal jejunal O 2 consumption (mol/min per kg BW) was lower ( P=0.02) in the R group when compared with the CON group. At day 140, maternal hepatic weight (g) was lower ( P=0.02) in RC and RR cows when compared with CC, and fetal jejunual O 2 consumption (mmol/min per mg tissue and mmol/min per g protein) was greater ( P⩽0.02) in RC when compared with RR. At day 254, maternal hepatic O 2 consumption (absolute and relative to BW) was lower ( P⩽0.04) in the RCC cows when compared with RRC. Fetal hepatic weight was lower ( P=0.05) in the CCC group when compared with RCC and RRC. The changes in response to nutrient restriction and realimentation in both the dam and fetus may indicate an adaptation to a lower amount of available nutrients by altering tissue mass and metabolism. 相似文献
11.
In his well-known essay, ??What Is a Sign???( CP 2.281, 285) Peirce uses ??likeness?? and ??resemblance?? interchangeably in his definition of icon. The synonymity of the two words has rarely, if ever, been questioned. Curiously, a locus classicus of the pair, at least in F. M. Cornford??s English translation, can be found in a late dialogue of Plato, namely, the Sophist. In this dialogue on the myth and truth of the sophists?? profession, the mysterious ??stranger??, who is most likely Socrates?? persona, makes the famous distinction between eikon (likeness) and phantasma (semblance) (236a,b). For all his broad knowledge in ancient philosophy, Peirce never mentioned this parallel; nor has any Peircean scholar identified it. There seems to be little problem with eikon as likeness, but phantasma may give rise to a puzzle which this paper will attempt to solve. Plato uses two pairs of words: what eikon is to phantasma is eikastikén (the making of likeness [235d]) to phantastikén (semblance making [236c]). In other words, icons come into being because of the act of icon-making, which is none other than indexicality. Witness what Peirce says about the relationship between photographs and the objects they represent: ??But this resemblance is due to the photographs having been produced under such circumstances that they were physically forced to correspond point by point to nature.?? (Ibid.) Thus the iconicity which links the representamen (sign) and its object is made possible not only by an interpretant, but also by idexisation. Their possible etymological and epistemological links aside, the Peircean example of photographing and the Platonic discussion of painting and sculpturing in the Sophist, clearly show the physio-pragmatic aspect of iconicity. The paper will therefore reread the Peircean iconicity by closely analysing this relatively obscure Platonic text, and by so doing restore to the text its hidden semiotic dimension. 相似文献
12.
The ability of biomolecules to fold and to bind to other molecules is fundamental to virtually every living process. Advanced experimental techniques can now reveal how single biomolecules fold or bind against mechanical force, with the force serving as both the regulator and the probe of folding and binding transitions. Here, we present analytical expressions suitable for fitting the major experimental outputs from such experiments to enable their analysis and interpretation. The fit yields the key determinants of the folding and binding processes: the intrinsic on-rate and the location and height of the activation barrier.Dynamic processes in living cells are regulated through conformational changes in biomolecules—their folding into a particular shape or binding to selected partners. The ability of biomolecules to fold and to bind enables them to act as switches, assembly factors, pumps, or force- and displacement-generating motors ( 1). Folding and binding transitions are often hindered by a free energy barrier. Overcoming the barrier requires energy-demanding rearrangements such as displacing water from the sites of native contacts and breaking nonnative electrostatic contacts, as well as loss of configurational entropy. Once the barrier is crossed, the folded and bound states are stabilized by short-range interactions: hydrogen bonds, favorable hydrophobic effects, and electrostatic and van der Waals attractions ( 2).Mechanistic information about folding and binding processes is detailed in the folding and binding trajectories of individual molecules: observing an ensemble of molecules may obscure the inherent heterogeneity of these processes. Single-molecule trajectories can be induced, and monitored, by applying force to unfold/unbind a molecule and then relaxing the force until folding or binding is observed ( 3–5) (). Varying the force relaxation rate shifts the range of forces at which folding or binding occurs, thus broadening the explorable spectrum of molecular responses to force and revealing conformational changes that are otherwise too fast to detect. The measured force-dependent kinetics elucidates the role of force in physiological processes ( 6) and provides ways to control the timescales, and even the fate, of these processes. The force-dependent data also provides a route to understanding folding and binding in the absence of force—by extrapolating the data to zero force via a fit to a theory. Open in a separate windowSchematic of the output from a force-relaxation experiment. The applied force is continuously relaxed from the initial value F0 until the biomolecule folds or binds, as signified by a sharp increase in the measured force. From multiple repeats of this experiment, distributions of the folding or binding forces are collected ( inset). Fitting the force distributions with the derived analytical expression yields the key parameters that determine the kinetics and energetics of folding or binding.In this letter, we derive an analytical expression for the distribution of transition forces, the major output of force-relaxation experiments that probe folding and binding processes. The expression extracts the key determinants of these processes: the on-rate and activation barrier in the absence of force. The theory is first developed in the context of biomolecular folding, and is then extended to cover the binding of a ligand tethered to a receptor. In contrast to unfolding and unbinding, the reverse processes of folding and binding require a theory that accounts for the compliance of the unfolded state, as well as the effect of the tether, to recover the true kinetic parameters of the biomolecule of interest.In a force-relaxation experiment, an unfolded biomolecule or unbound ligand-receptor complex is subject to a stretching force, which is decreased from the initial value F0 as the pulling device approaches the sample at speed V until a folding or binding transition is observed () ( 3–5). Define S( t) as the probability that the molecule has not yet escaped from the unfolded (implied: or unbound) state at time t. When escape is limited by one dominant barrier, S( t) follows the first-order rate equation where k←( F( t)) is the on-rate at force F at time t. Because, prior to the transition, the applied force decreases monotonically with time, the distribution of transition forces, p( F), is related to S( t) through , yielding (1)Here is the force relaxation rate. The proper normalization of p( F) is readily confirmed by integrating Eq. 1 from the initial force F0 to negative infinity, the latter accounting for transitions that do not occur by the end of the experiment. Note that the expression for the distribution of folding/binding forces in Eq. 1 differs from its analog for the unfolding process ( 7) by the limits of integration and a negative sign, reflecting the property of a relaxation experiment to decrease the survival probability S( t) by decreasing the force. Converting the formal expression in Eq. 1 into a form suitable for fitting experimental data requires establishing functional forms for k←( F) and and analytically solving the integral. These steps are accomplished below.The on-rate k←( F) is computed by treating the conformational dynamics of the molecule as a random walk on the combined free energy profile G( x, t) = G0( x) + Gpull( x, t) along the molecular extension x. Here G0( x) is the intrinsic molecular potential and Gpull( x, t) is the potential of the pulling device. When G( x, t) features a high barrier on the scale of kBT ( kB is the Boltzmann constant and T the temperature), the dynamics can be treated as diffusive. The unfolded region of the intrinsic potential for a folding process, unlike that for a barrierless process ( 8), can be captured by the function which has a sharp (if ν = 1/2, , inset) or smooth (if ν = 2/3) barrier of height Δ G‡ and location x‡. The potential of a pulling device of stiffness κS is Gpull( x, t) = κS/2( X0 – Vt – x) 2 with an initial minimum at X0 (corresponding to F0). Applying Kramers formalism ( 9) to the combined potential G( x, t), we establish the analytical form of the on-rate at force F( t), where k0 is the intrinsic on-rate, β ≡ ( kBT) −1, and is the stiffness of the unfolded biomolecule under force F (see the Supporting Material for details on all derivations). The full nonlinear form of Gpull( x, t) was necessary in the derivation because, in contrast to the typically stiff folded state, the unfolded state may be soft (to be exact, 1/2 κS
x‡2( F) << kBT may not be satisfied) and thus easily deformed by the pulling device. Because of this deformation, the folding transition faces an extra contribution (regulated by the ratio κS/ κU( F)) to the barrier height, typically negligible for unfolding, that decreases the on-rate in addition to the applied force F. Open in a separate windowContributions to the free energy profile for folding ( inset) and binding ( main figure). The derived expression ( Eq. 2) extracts the on-rate and the location and height of the activation barrier to folding. When applied to binding data, the expression extracts the parameters of the ligand-tether-receptor (LTR) potential ( x); the proposed algorithm ( Eqs. 3 and 4) removes the contribution of the tether potential Gteth(x) to recover the parameters of the intrinsic ligand-receptor (LR) potential G0( x).The last piece required for Eq. 1, the loading rate , is computed as the time derivative of the force F( t) on the unfolded molecule at its most probable extension at time t: Finally, we realize that the integral in Eq. 1 can be solved analytically exactly, both for ν = 1/2 and ν = 2/3, resulting in the analytical expression for the distribution of folding forces: (2) Equation 2 can be readily applied to (normalized) histograms from force-relaxation experiments to extract the parameters of the intrinsic kinetics and energetics of folding. Being exact for ν = 1/2 and ν = 2/3, Eq. 2 is also an accurate approximation for any ν in the interval 1/2 < ν < 2/3 as long as κS ≲ κU ( F) (see Fig. S1 in the Supporting Material). For simplicity, in Eq. 2 we have omitted the term containing F0 as negligible if F0 is large enough to prevent folding events.The solution in Eq. 2 reveals properties of the distribution of folding forces that distinguish it from its unfolding counterpart ( 7): - 1.The distribution has a positive skew (), as intuitively expected: the rare folding events occur at high forces when the barrier is still high.Open in a separate windowForce histograms from folding (left) and binding (right) simulations at several values of the force-relaxation speed (in nanometers per second, indicated at each histogram). Fitting the histograms with the analytical expression in Eq. 2 (lines) recovers the on-rate and activation barrier for folding or binding (): faster force relaxation leaves less time for thermal fluctuations to push the system over a high barrier, causing transitions to occur later (i.e., at lower forces), when the barrier is lower.
- 3.The stiffness κS and speed V enter Eq. 2 separately, providing independent routes to control the range of folding forces and thus enhance the robustness of a fit.
The application of the above framework to binding experiments on a ligand and receptor connected by a tether ( 3) involves an additional step—decoupling the effect of the tether—to reconstruct the parameters of ligand-receptor binding. Indeed, the parameters extracted from a fit of experimental histograms to Eq. 2 characterize the ligand-tether-receptor (LTR) potential ( , , , ν) (). The parameters of the natural ligand-receptor (LR) potential ( k0, x‡, Δ G‡) can be recovered using three characteristics of the tether: contour length L; persistence length p; and extension Δℓ of the tether along the direction of the force in the LTR transition state. The values of L and p can be determined from the force-extension curve of the tether ( 10); these define the tether potential Gteth( x) (). The value of Δℓ can be found from an unbinding experiment ( 7) on LTR and the geometry of the tether attachment points (see Fig. S3). Approximating the region of the LR potential between the transition and unbound states as harmonic, with no assumptions about the shape of the potential beyond x‡, the ligand-receptor barrier parameters are then (3)and the intrinsic unimolecular association rate is (4)Here, the force value is extracted from the force-extension curve of the tether at extension and where Gteth( x) is the wormlike-chain potential (see Eq. S13 in the Supporting Material). Equations 3–4 confirm that a tether decreases the height and width of the barrier (see ), thus increasing the on-rate.In , the developed analytical framework is applied to folding and binding force histograms from Brownian dynamics simulations at parameters similar to those in the analogous experimental and computational studies ( 3,5,11) (for details on simulations and fitting procedure, see the Supporting Material). For the stringency of the test, the simulations account for the wormlike-chain nature of the molecular unfolded and LTR unbound states that is not explicitly accounted for in the theory. With optimized binning ( 12) of the histograms and a least-squares fit, Eqs. 2–4 recover the on-rate, the location and the height of the activation barrier, and the value of ν that best captures how the kinetics scale with force ( Eq. 2Folding | k0 (s−1) | x‡ (nm) | ΔG‡ (kBT) | ν | True | 9.5 × 103 | 2.2 | 2.0 | — | Fit | 8 ± 2 × 103 | 2.2 ± 0.2 | 1.8 ± 0.5 | 0.54a | Binding (LTR) | (s−1) | (nm) | (kBT) | ν | True | 28 | 1.56 | 1.7 | — | Fit | 24 ± 3 | 1.57 ± 0.09 | 1.8 ± 0.4 | 0.53a | Binding (LR) | k0 (s−1) | x‡ (nm) | ΔG‡ (kBT) | — | True | 2.8 | 3.0 | 4.0 | — | Fit | 2.7 ± 0.2 | 2.9 ± 0.1 | 4.1 ± 0.1 | — | Open in a separate windowaFixed at value that minimized least-squares error. 相似文献
13.
By means of contact angle determinations with two liquids, on hydrated as well as on dried protein layers, the long-range and the short-range contributions to the protein surface tensions, and from these the protein ( G
131) and the protein-ligand ( G
132) free energies of interaction in aqueous media, were determined. For human serum albumin (HSA), human IgG, and human IgA, the differences between G
131
HYDRATED
and G
131
DRY
were connected with the behavior of these proteins in low concentrations of (NH 4) 2SO 4 versus saturated (NH 4) 2SO 4 solutions. By interpolation, intermediate points are found that correlate well with the known salting-out properties of these three proteins. On the basis of the data, it is predicted that the precipitation of IgG by 1/3 saturated (NH 4) 2SO 4 is preventable, or reversible, by the admixture of 15% dimethylsulfoxide; both predictions are confirmed experimentally. From the G
132 values found, it is shown that HSA and IgG should attach to phenyl ligands under physiological conditions, but that IgA is so hydrophilic that it only can adhere to phenyl ligands after partial dehydration brought about when admixed with 1 M (NH 4) 2SO 4. Closer analysis of the values obtained for the long-range and short-range components of the surface tensions of HSA, IgG, and IgA allow deeper insight into their functional, chemical, and physicochemical properties. 相似文献
14.
Gomesin ( Gm) was the first antimicrobial peptide (AMP) isolated from the hemocytes of a spider, the Brazilian mygalomorph Acanthoscurria gomesiana. We have been studying the properties of this interesting AMP, which also displays anticancer, antimalarial, anticryptococcal and anti‐ Leishmania activities. In the present study, the total syntheses of backbone‐cyclized analogues of Gm (two disulfide bonds), [Cys(Acm) 2,15]‐ Gm (one disulfide bond) and [Thr 2,6,11,15,d ‐Pro 9]‐ Gm (no disulfide bonds) were accomplished, and the impact of cyclization on their properties was examined. The consequence of simultaneous deletion of pGlu 1 and Arg 16‐Glu‐Arg 18‐NH 2 on Gm antimicrobial activity and structure was also analyzed. The results obtained showed that the synthetic route that includes peptide backbone cyclization on resin was advantageous and that a combination of 20% DMSO/NMP, EDC/HOBt, 60 °C and conventional heating appears to be particularly suitable for backbone cyclization of bioactive peptides. The biological properties of the Gm analogues clearly revealed that the N‐terminal amino acid pGlu 1 and the amidated C‐terminal tripeptide Arg 16‐Glu‐Arg 18‐NH 2 play a major role in the interaction of Gm with the target membranes. Moreover, backbone cyclization practically did not affect the stability of the peptides in human serum; it also did not affect or enhanced hemolytic activity, but induced selectivity and, in some cases, discrete enhancements of antimicrobial activity and salt tolerance. Because of its high therapeutic index, easy synthesis and lower cost, the [Thr 2,6,11,15,d ‐Pro 9]‐ Gm analogue remains the best active Gm‐derived AMP developed so far; nevertheless, its elevated instability in human serum may limit its therapeutic potential. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
15.
Objective: This study was conducted to evaluate the association of total and central adiposity with serum cardiovascular disease (CVD) risk factors in lean and obese Portuguese children and adolescents. Research Methods and Procedures: A total of 87 girls (13.2 ± 1.6 years old, 29.9 ± 6.4% body fat [mean ± SD]) and 72 boys (13.2 ± 1.6 years old, 20.8 ± 9.9% body fat) volunteered for the study. Whole‐body composition and fat distribution, from DXA and anthropometry, and serum lipids, lipoproteins, and apolipoproteins were evaluated. Results: The sum of three trunk skinfolds (STS) was highly correlated with total trunk fat mass measured by DXA ( p < 0.001). Body mass index, DXA‐measured percentage of body fat, trunk fat mass, STS, and the waist‐to‐height ratio were generally found to be associated with triacylglycerol, the ratio of total cholesterol (TC) to high density lipoprotein‐cholesterol (HDL‐C), low density lipoprotein‐cholesterol (LDL‐C), and apolipoprotein B levels, (significant age‐adjusted r between 0.16 and 0.27, p < 0.05). Body mass index, STS, and the waist circumference were also associated with HDL‐C ( p < 0.05), whereas no body composition variable significantly correlated with TC or apolipoproteins A‐I. The STS was significantly correlated with HDL‐C ( p < 0.01), TC/HDL‐C ( p < 0.05), and apolipoproteins A‐I ( p < 0.05) independently of whole‐body fatness. Obese subjects ( n = 73) had higher TC, LDL‐C, TC/HDL‐C, and apolipoprotein B than did non‐obese subjects ( n = 86), and significant associations between central adiposity and some lipid variables (triacylglycerol and HDL‐C) were found in obese children and adolescents that were not present in leaner individuals. Discussion: DXA‐ and anthropometry‐based whole‐body and central fat measures are associated with serum CVD risk factors in Portuguese boys and girls. Obese children and adolescents have a poorer lipid profile than do their leaner counterparts. Trunk skinfolds, which are easy to obtain even in large samples, predict CVD risk factors to the same extent as DXA‐based variables, in some cases, independently of total fatness. 相似文献
16.
The aim of the present study was to measure zinc (Zn) and iron (Fe) concentration in human semen and superoxide dismutase
(SOD) activity in seminal plasma and correlate the results with sperm quality. Semen samples were obtained from men ( N = 168) undergoing routine infertility evaluation. The study design included two groups based on the ejaculate parameters.
Group I ( n = 39) consisted of males with normal ejaculate (normozoospermia), and group II ( n = 129) consisted of males with pathological spermiogram. Seminal Zn and Fe were measured in 162 samples (group I, n = 38; group II, n = 124) and SOD activity in 149 samples (group I, n = 37; group II, n = 112). Correlations were found between SOD activity and Fe and Zn concentration, and between Fe and Zn concentration. SOD
activity was negatively associated with volume of semen and positively associated with rapid progressive motility, nonprogressive
motility, and concentration. Negative correlation was stated between Fe concentration and normal morphology. Mean SOD activity
in seminal plasma of semen from men of group I was higher than in seminal plasma of semen from men of group II. Fe concentration
was higher in teratozoospermic males than in males with normal morphology of spermatozoa in group II. Our results suggest
that Fe may influence spermatozoa morphology. 相似文献
17.
Temperature regulation and oxygen consumption were examined in two species of grasshoppers: Melanoplus sanguinipes from cold alpine tundra at elevation 3,800 m, and Trimerotropis pallidipennis from hot desert habitats at elevation 250 m. Both species utilized behavioral thermoregulation to keep body temperature ( T b ) more constant than environmental temperatures ( T e ) during the day. The difference in average T b in the two species was much less than the difference in T e 's. Microclimate measurements indicate that temperature regulation is not difficult for M. sanguinipes, but T. pallidipennis must restrict activity for much of the day to avoid heat stress and can easily overheat if it moves into sunlit areas. Oxygen consumption ( \(\dot V{\text{O}}_{\text{2}} \) ) at average T b and total daily energy expenditures are higher in M. sanguinipes than in T. pallidipennis, as is the Q 10 for \(\dot V{\text{O}}_{\text{2}} \) . These differences may be related to different strategies for energy utilization and predator avoidance. 相似文献
18.
Ovule and especially seed anatomy of eight species of Cochlospermaceae, Bixaceae, Cistaceae, Monotoideae, Pakaraimaeoideae (two subfamilies of Dipterocarpaceae), and Sarcolaenaceae were investigated. All representatives show a bixoid chalazal region in the seed as probable exclusive synapomorphy among angiosperms. The palisade layer of the exotegmen is curved inwards at its proximal end and forms a dome-shaped structure. A plug of hypostase tissue with an annulus/core structure fits into this dome. Moreover, two additional tissue types in the hypostase can be found in some representatives of the group. These and other micromorphological, wood anatomical, and floral morphological characters, indicate that the taxa form a monophyletic group close to Malvales s. str. The form of the starch grains in the endosperm is compared and is described for the first time for Pakaraimaea ( Dipterocarpaceae) and Leptolaena ( Sarcolaenaceae). The position of Diegodendron close to Bixa and the presumably more distant positions of Muntingia and Neuradaceae are discussed. 相似文献
19.
Dogs and cats are the only domestic animals that still routinely reside in the same domicile as their owners around the world, and hence the interest in their role as reservoirs of potentially zoonotic agents. In the case of cryptosporidiosis and giardiasis, current data suggests that dogs and cats do not routinely share their infections with healthy people. Dogs are hosts of Cryptosporidiumcanis and Giardiaduodenalis Assemblages C and D. Cats are hosts to Cryptosporidiumfelis and G. duodenalis Assemblage F. Dogs and cats (and other animals) are sometimes infected with sub-Assemblage AI, an Assemblage also found in people, but people usually have sub-Assemblage AII. Unfortunately, severely immunocompromised individuals and malnourished children can be made ill by infections with C. canis and C. felis. People should practice good sanitation and hygiene to minimize environmental contamination and contact with the infectious (oo)cysts that may be shed by their pets. 相似文献
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