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1.
The changes in polymer-solvent interactions that occur when native calf thymus DNA is dialyzed against Na2SO4 solutions of a given ionic strength and buffer concentration but of varying concentrations in methylmercuric hydroxide have been investigated with the help of solution density measurements at 25 °C and pH 6.8–7.0. From measurements executed under equilibrium dialysis conditions at the three salt levels 5 mm, 0.05 m, and 0.5 m Na2SO4 (m refers to molality) and in the presence of 5 mm cacodylic acid buffer, the density increments (???c2)μ0 for native calf thymus DNA were determined as a function of CH3HgOH concentration. (???c2)μ0 was found not to vary with organomercurial concentration, irrespective of the concentration of supporting electrolyte, until a certain CH3HgOH concentration level has been reached, viz., pM1 ? 3.5 (pM1 = ?log mCH3HgOH), beyond which (???c2)μ0 increases strongly with increasing concentration of CH3HgOH. As is shown by optical melting, (???c2)μ0 becomes a function of organomercurial concentration the moment DNA undergoes denaturation brought about by the complexing of CH3HgOH with the various N-binding sites of the base residues in the DNA double helix.Polymer-solvent interactions, expressed in terms of preferential water interactions (“net hydration”) and preferential salt interactions (“salt solvation”), were derived from the (???c2)μ0 data in combination with data obtained on the preferential interaction of CH3HgOH with denatured DNA and data on the partial specific volumes of all major solution components, gathered from density measurements on solutions with fixed concentrations of diffusible components. Evidence is presented which shows that denaturation in general decreases the net hydration while salt becomes preferentially associated with the polyelectrolyte. This process is further amplified by the interaction of CH3HgOH with denatured DNA: Methylmercurated DNA alters the redistribution of diffusible components at dialysis equilibrium to such an extent that in a formal sense large amounts of water are rejected from the immediate vicinity of the polymer. The molecular implications of these findings are explored. The results are further discussed in the light of previous findings where the methylmercury-induced denaturation of DNA had been studied with the help of buoyant density measurements in a Cs2SO4 density gradient and by velocity-sedimentation in a variety of sulfate media.  相似文献   

2.
3.
Using the adsorption theory of chemical kinetics, a new equation concerning the growth of single populations is presented:
dXdt =μcX(1 ?)XXm1?XXm
or in its integral form:
lnXXo?lnXm?XXm?Xo+XmXmXm?XXm?Xoc(t?to)
This equation attempts to explain the relationship between population increment and limiting resources. It can be reduced to either the logistic or exponential equation under two extreme conditions. The new equation has three parameters, Xm, Xm and μc, each of which has ecological significance. XmX′m concerns the efficiency of nutrient utilization by an organism. Its value is between zero and one. With ratios approaching unity, the efficiency is high; lower ratios indicate that population increment is quickly restricted by limiting resources. μc, is a velocity parameter lying between μe, (exponential growth) and μL (logistic growth), and is dependent on the value of solXmX′m. From μc we can predict the time course of population incremental velocity (dXdt), and can observe that it is not symmetrical, unlike that derived from the logistic equation. At XmX′m = 1 the maximum velocity of the population increment predicted from the new equation is twice that of the logistic equation.Population growth in nature seems to support the new equation rather than the logistic equation, and it can be successfully fitted by means of a least square method.  相似文献   

4.
(1) Aqueous solutions of 1–10 μM ferricytochrome c treated with 100 μM–100 mM H2O2 at pH 8.0 emit chemiluminescence with quantum yield Ф ? 10?9 and absolute maximum intensity Imax ? 105 hv/s per cm3 (λ = 440), and exhibit exponential decay with a rate constant of 0.15 s?1. (2) The emission spectrum of the chemiluminescence covers the range 380–620 nm with the maximum at 460 ± 10 nm. (3) Neither cytochrome c nor haemin fluoresce in the spectral region of the chemiluminescence. In the reaction course with H2O2, a weak fluorescence in the region 400–620 nm with λmax = 465–510 nm (λexc 315–430 nm) gradually arises. This originates from tryptophan oxidation products of the formylkynurenine type or from imidazole derivatives, respectively. (4) Frozen solutions (77 K) of cytochrome c exhibit phosphorescence typical of tryptophan (λexc = 280 nm, λem = 450 nm). During the peroxidation, an additional phosphorescence gradually appears in the range 480–620 nm with λmax = 530 nm (λexc = 340 nm). This originates from oxidative degradation products of tryptophan. (5) There are no red bands in the chemiluminescence spectra of cytochrome c or haemin. This result suggests that singlet molecular oxygen O2(1Δg) is not involved in either peroxidation or chemiluminescence. (6) The haem Fe3+ group and H2O2 appear to be crucial for the chemiluminescence. It is suggested that the generation of electronically excited, light-emitting states is coupled to the production of conformational out-of-equilibrium states of peroxy-Fe-protoporphyrin IX compounds.  相似文献   

5.
(1) The polymorphic phase behaviour of aqueous dispersions of various synthetic phosphatidylethanolamines, both singly and in mixtures, has been investigated by 31P-NMR. (2) 14:014:0 PE remains in the lamellar phase up to 90°C. 18:1t18:1t PE exhibits a lamellar to hexagonal (HII) transition between 60°C and 63°C. For 18:1c18:1c PE, the lamellar to hexagonal (HII) transition occurs between 7 and 12°C, whereas for 18:2c18:2c PE, the hexagonal (HII) phase is the preferred structure above ?15°C. (3) Mixtures of 18:1c18:1c PE and 18:1t18:1t PE exhibit near-ideal miscibility behaviour. For mixtures of 18:1c18:1c PE and 14:014:0 PE there is evidence of fluid-solid immiscibility at temperatures below the gel-liquid crystalline transition temperature of the 14:014:0 PE component. Mixtures of 18:2c18:2c PE and 18:1t18:1t PE exhibit complex phase behaviour involving limited fluid-solid immiscibility at low temperatures and formation of a phase allowing isotropic motional averaging at higher temperatures. (4) 31P-NMR provides a graphic method for investigating the miscibility properties of mixed PE systems.  相似文献   

6.
The oxygen dependence of cellular energy metabolism.   总被引:14,自引:0,他引:14  
Suspensions of cultured C 1300 neuroblastoma cells, sarcoma 180 ascites tumor cells, and Tetrahymena pyriformis cells were used to study the oxygen dependence of cellular energy metabolism. Cellular respiration was found to be almost independent of oxygen tension to values of less than 20 μm with an apparent Km for oxygen of less than 1 μm. In contrast, the reduction of mitochondrial cytochrome c was found to be dependent on oxygen tension at all values from 240 μm downward. Oxygen dependence was also observed in terms of cellular energy metabolism expressed as adenosine triphosphate and adenosine diphosphate concentrations. These data provide direct evidence that in intact cells mitochondrial oxidative phosphorylation is oxygen dependent throughout the physiological range of oxygen tension (air saturation and below). The respiratory rate is maintained constant when the oxygen tension is lowered by decreasing values of the cytosolic [ATP][ADP][Pi] and intramitochondrial [NAD]+][NADH] because these regulatory parameters adjust to maintain a constant rate of ATP synthesis. The lack of oxygen dependence in the respiratory rate means that the rate of cellular ATP utilization is essentially oxygen independent until the mitochondria can no longer synthesize ATP at the required rate and [ATP][ADP][Pi].  相似文献   

7.
In the presence of the Na+-channel blocker amiloride, the short-circuit current across the skins of bullfrog tadpoles in metamorphic stages XIX–XXIV was subjected to fluctuation analysis. The resulting power spectra contained a Lorentzian component of which the plateau value (S0) decreased while the corner frequency (fc) increased as the mucosal amiloride concentration was increased from 0.5 to 24 μM. From the linear relationship between the fc values and the amiloride concentrations it was possible to determine the binding (k′01) and unbinding (k10) constants for amiloride to its receptor on the Na+ channel. With these parameters as well as short-circuit current and S0 values, the current through the individual Na+ channels (i) was calculated (average 0.58 pA). It did not increase significantly during late metamorphosis. The density of Na+ channels (M) in the apical membrane, on the other hand, increased significantly. It would appear that the increase in short-circuit current which occurs at this time is due primarily to an increase in amiloride-blockable Na+ channels. Unexpectedly, a Lorentzian component could be fitted to power spectra in amiloride-treated skins (stages XIX–XXI) which showed no amiloride-sensitive short-circuit current. Moreover, the typical increase in fc with the amiloride concentration did not occur in these animals.  相似文献   

8.
9.
The flow measurement of each component in each compartment is important in works on transport phenomena in a biological system. The method of flow measurement was studied adopting the capacitor concept derived from network thermodynamics.A biologically active component i in a compartment is defined as follows,
ni=n1+n2=c1V+c2V
where the total quantity ni consists of a measurable form ni (free form, conc. c1) and concealed form n2 (conc, c2). Capacitor for the species i of a compartment is defined as follows,
C=dnidμi=1+c2c1c1dVi+1+dc2dc1vdc1i
,
=Ac1dVi+BVdc1dt
Thus flow of each component is expressed as,
Ji=dnidi=dniinidt=Cdμidt
,
=Ac1dVdt+BVdc1dt
Method of determination of capacitor coefficients A and B by titration experiment was also considered. For an experimental case, the capacitance for H+ of blood compartment was determined. The relationship between the capacitor concept and the buffer value of Van Slyke was discussed.  相似文献   

10.
1. In mitochondrial particles antimycin binds to two separate specific sites with dissociation constants Kd1 ≦ 4 · 10?13M and Kd2 = 3 · 10?9M, respectively.2. The concentrations of the two antimycin binding sites are about equal. The absolute concentration for each binding site is about 100 – 150 pmol per mg of mitochondrial protein.3. Antimycin bound to the stronger site mainly inhibits NADH- and succinate oxidase. Binding of antimycin to the weaker binding site inhibits the electron flux to exogenously added cytochrome c after blocking cytochrome oxidase by KCN.4. Under certain conditions cytochrome b and c1 are dispensible components for antimycin-sensitive electron transport.5. A model of the respiratory chain in yeast is proposed which accounts for the results reported here and previously. (Lang, B., Burger, G. and Bandlow, W. (1974) Biochim. Biophys. Acta 368, 71–85).  相似文献   

11.
Infinite cis uptake of cyclic AMP into red blood cell ghosts has been measured. The Kicoi is calculated from two different integrated rate equations that are applicable when the substrate concentration is unsufficient to cause volume changes. Values of 0.69 mM and 0.66 mM are obtained for the infinite cisKm at 30°C using these procedures. These values are only slightly higher than that predicted from zero trans net flux experiments.Lowering the temperature reduces Kicoi from 0.69 mM at 30°C to 0.478 mM at 20°C, 0.108 mM at 10°C and 0.072 mM at 4°C (Q10 = 2.4). The Q10 for activation of influx permeability of 10?5 M cyclic AMP is 1.55.  相似文献   

12.
The maximum slope of the plot, appearing in the paper of Watari & Isogai (1976), was derived algebraically as a function of allosteric constants c and αmor βm (= m), and the relation between L, c, and αmor βm, was also obtained, where L = ToRo, c = KRKT, αm = FmKR, βm = FmKT, Roand To are concentrations of unligated R and T states respectively, KRand KT are microscopic dissociation constants, and Fm is the ligand concentration at the maximum slope of the plot. When the maximum slope is increased by one, the value becomes Hill constant, n. Nomographs which enable easier estimation of allosteric constants, L and c, were constructed from the two given values, the maximum slope of the plot, n ? 1, and αmor βm, in the cases where the maximum number of ligands, N, was 2 and 4. In the nomograph, log c is plotted against log L2cN keeping the value of the maximum slope of the plot and that of αmor βm constant. These nomographs show that the representation is symmetrical in the cases of L2cN > 1 and L2cN < 1.  相似文献   

13.
S.P.J. Brooks  P. Nicholls 《BBA》1982,680(1):33-43
Citrate and other polyanion binding to ferricytochrome c partially blocks reduction by ascorbate, but at constant ionic strength the citrate-cytochrome c complex remains reducible; reduction by TMPD is unaffected. At a constant high ionic strength citrate inhibits the cytochrome c oxidase reaction competitively with respect to cytochrome c, indicating that ferrocytochrome c also binds citrate, and that the citrateferrocytochrome c complex is rejected by the binding site at high ionic strength. At lower ionic strengths, citrate and other polyanions change the kinetic pattern of ferrocytochrome c oxidation from first-order towards zero-order, indicating preferential binding of the ferric species, followed by its exclusion from the binding site. The turnover at low cytochrome c concentrations is diminished by citrate but not the Km (apparent non-competitive inhibition) or the rate of cytochrome a reduction by bound cytochrome c. Small effects of anions are seen in direct measurements of binding to the primary site on the enzyme, and larger effects upon secondary site binding. It is concluded that anion-cytochrome c complexes may be catalytically competent but that the redox potentials and/or intramolecular behaviour of such complexes may be affected when enzyme-bound. Increasing ionic strength diminishes cytochrome c binding not only by decreasing the ‘association’ rate but also by increasing the ‘dissociation’ rate for bound cytochrome c converting the ‘primary’ (T) site at high salt concentrations into a site similar kinetically to the ‘secondary’ (L) site at low ionic strength. A finite Km of 170 μM at very high ionic strength indicates a ratio of KMK0M of about 5000. It is proposed that anions either modify the E10 of cytochrome c bound at the primary (T) site or that they perturb an equilibrium between two forms of bound c in favour of a less active form.  相似文献   

14.
Somatic (cs) and a testis-specific (ct I) cytochromes c were purified to homogeneity from rat tissues (heart, liver, kidney, and testis). The purification procedure involved (1) homogenization of tissues at pH 4.5, (2) treatment with methanol-chloroform solvents, (3) hydroxylapatite column chromatography, (4) carboxymethyl-cellulose column chromatography, and (5) Sephacryl S-200 gel filtration. The isolated cytochromes c were free from polymeric and other “modified” forms, and did not bind CO, azide, or cyanide. The absorption maxima and the molecular weights of both cytochromes cs and ct I were identical. The ratio of A549.5 nm(reduced)A280 nm(oxidized) for cytochromes cs averaged 1.28. The unique properties of cytochrome ct I, compared to somatic cytochrome c, were as follows: (1) different elution profiles from hydroxylapatite and carboxymethyl-cellulose column chromatography experiments, (2) less basic intrinsic molecular charge shown by the slow mobility in native polyacrylamide gel electrophoresis, (3) probable asymmetric molecular shape as evidenced from gel filtration experiments, (4) significantly higher millimolar extinction coefficient values (33.6 at 549.5 nm), (5) a low ratio (1.04) of A549.5 nm(reduced)A280 nm(oxidized), and (6) difference of about 20 amino acid residues per mole.  相似文献   

15.
(1) Analysis of the data from steady-state kinetic studies shows that two reactions between cytochrome c and cytochrome c oxidase sufficed to describe the concave Eadie-Hofstee plots (Km ? 1 · 10?8M and Km ? 2 · 10?5M). It is not necessary to postulate a third reaction of Km ? 10?6M. (2) Change of temperature, type of detergent and type of cytochrome c affected both reactions to the same extent. The presence of only a single catalytic cytochrome c interaction site on the oxidase could explain the kinetic data. (3) Our experiments support the notion that, at least under our conditions (pH 7.8, low-ionic strength), the dissociation of ferricytochrome c from cytochrome c oxidase is the rate-limiting step in the steady-state kinetics. (4) A series of models, proposed to describe the observed steady-state kinetics, is discussed.  相似文献   

16.
The α-chymotrypsin-catalyzed hydrolysis rates of p-nitrophenyl cyclopentane-carboxylate (I), p-nitrophenyl indan-2-carboxylate (II), and p-nitrophenyl spiro-[4.4]nonane-2-carboxylate (III) were measured at pH 8.1 in 20% methanol. After correction for variations in reactivity owing to stereoelectronic effects inherent to the substrates, the deacylation rate constants (kc)n of I and II are not significantly different. In (kcKm)n II is 50 times more reactive than I, which demonstrates that the aromatic ring of the former substrate contributes significantly to its reactivity. The nearly equal reactivities of II and III indicate that the enzyme is rather insensitive to the geometry of the nonester-bearing ring of these compounds.  相似文献   

17.
Three chlorophyll-protein complexes of a Chroomonas species (Cryptophyceae) have been separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis. The two bands at 100 and 42 kDa are Complex I (CP I) and Complex IV (CP IV), the ubiquitous chlorophyll a-proteins associated with Photosystems I and II, respectively. The third 55 kDa band, which had two peptide subunits (24 and 20 kDa), contained both chlorophyll a and chlorophyll c2 in a molar ratio of 1.4 chlorophyll a to 1 chlorophyll c2 (chlorophyll achlorophyll c2 ratio in whole cells = 4). A chlorophyll ac2 fraction with similar spectral and electrophoretic properties was isolated by digitonin-sucrose density gradient centrifugation. This fraction had no photochemical activity and contained only a single carotenoid species with absorbance maxima in methanol at 424, 448 and 476 nm. Efficient energy transfer from chlorophyll c2 to chlorophyll a occurred in the complex.  相似文献   

18.
Joël Lunardi  Pierre V. Vignais 《BBA》1982,682(1):124-134
(1) N-4-Azido-2-nitrophenyl-γ-[3H]aminobutyryl-AdoPP[NH]P(NAP4-AdoPP[NH]P) a photoactivable derivative of 5-adenylyl imidodiphosphate (AdoPP[NH]P), was synthesized. (2) Binding of 3H]NAP4-AdoPP[NH]P to soluble ATPase from beef heart mitochrondria (F1) was studied in the absence of photoirradiation, and compared to that of [3H]AdoPP[NH]P. The photoactivable derivative of AdoPP[NH]P was found to bind to F1 with high affinity, like AdoPP[NH]P. Once [3H]NAP4-AdoPP[NH]P had bound to F1 in the dark, it could be released by AdoPP[NH]P, ADP and ATP, but not at all by NAP4 or AMP. Furthermore, preincubation of F1 with unlabeled AdoPP[NH]P, ADP, or ATP prevented the covalent labeling of the enzyme by [3H]NAP4-AdoPP[NH]P upon photoirradiation. (3) Photoirradiation of F1 by [3H]NAP4-AdoPP[NH]P resulted in covalent photolabeling and concomitant inactivation of the enzyme. Full inactivation corresponded to the binding of about 2 mol [3H]NAP4-AdoPP[NH]Pmol F1. Photolabeling by NAP4-AdoPP[NH]P was much more efficient in the presence than in the absence of MgCl2. (4) Bound [3H]NAP4-AdoPP[NH]P was localized on the α- and β-subunits of F1. At low concentrations (less than 10 μM), bound [3H]NAP4-AdoPP[NH]P was predominantly localized on the α-subunit; at concentrations equal to, or greater than 75 μM, both α- and β-subunits were equally labeled. (5) The extent of inactivation was independent of the nature of the photolabeled subunit (α or β), suggesting that each of the two subunits, α and β, is required for the activity of F1. (6) The covalently photolabeled F1 was able to form a complex with aurovertin, as does native F1. The ADP-induced fluorescence enhancement was more severely inhibited than the fluorescence quenching caused by ATP. The percentage of inactivation of F1 was virtually the same as the percentage of inhibition of the ATP-induced fluorescence quenching, suggesting that fluorescence quenching is related to the binding of ATP to the catalytic site of F1.  相似文献   

19.
The meaning of compartmental concentration is intuitively simple in well-stirred compartment models with uniform concentration but not so in the general case. This meaning may be better understood by relating the general compartmental model to a spatially explicit one such as the Krogh cylinder model. We show that compartmental equations result directly by spatial averaging of the Krogh partial differential equations. Intercompartmental transport is usually stated as flux is proportional to the capillary-tissue concentration difference or J = ? (Cc - CT). We verify this simple equation by showing that flux in the Krogh model is also approximately first order and then derive the transport coefficient, ?, in terms of the geometry and diffusivity in the Krogh model. A relation between capillary and venous concentration or, for a gas, partial pressure is needed. For the highly diffusable, metabolic gas C02 this relation is Pc = Pv?M20Kc that is, capillary and venous partial pressures differ by one half the metabolic generation.  相似文献   

20.
A. Vermeglio  P. Joliot 《BBA》1984,764(2):226-232
Absorption changes, following a series of actinic flashes, linked to oxidoreduction states of ubiquinone, cytochrome ct together with the carotenoid bandshift, have been measured for intact cells of Rhodopseudomonas sphaeroides under aerobic conditions. Binary oscillations are observed for these different contributions: (1) about one molecule of ubisemiquinone and fully reduced quinone are formed on odd and even flashes, respectively; (2) cytochrome ct re-reduction is faster (t12 ≈ 50 ms) after an even number of flashes than after an odd number; (t12 ≈ 100 ms); (3) a slow-rising phase (t12 ≈ 5 ms, antimycin A-insensitive) of the carotenoid bandshift is observed after each even flash. These results are compared to the respiratory activity of the cells under flash excitation and discussed in relation to a model, in which respiratory and photosynthetic electron chains interact at the level of cytochrome c2 and where the terminal oxidase is supposed to have electrogenic properties.  相似文献   

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