共查询到20条相似文献,搜索用时 31 毫秒
1.
Kanakis CD Tarantilis PA Polissiou MG Diamantoglou S Tajmir-Riahi HA 《Cell biochemistry and biophysics》2007,49(1):29-36
In this report we are examining how the antioxidant flavonoids can prevent DNA damage and what mechanism of action is involved
in the process. Flavonoids are strong antioxidants that prevent DNA damage. The anticancer and antiviral activities of these
natural products are implicated in their mechanism of actions. We study the interactions of quercetin (que), kaempferol (kae),
and delphinidin (del) with DNA and transfer RNA in aqueous solution at physiological conditions, using constant DNA or RNA
concentration 6.25 mmol (phosphate) and various pigment/polynucleotide(phosphate) ratios of 1/65 to 1 (DNA) and 1/48 to 1/8
(tRNA). The structural analysis showed quercetin, kaempferol, and delphinidin intercalate DNA and RNA duplexes with minor
external binding to the major or minor groove and the backbone phosphate group with overall binding constants for DNA adducts
K
que = 7.25 (±0.65) × 104 M−1, K
kae = 3.60 (±0.33) × 104 M−1, and K
del = 1.66 (±0.25) × 104 M−1 and for tRNA adducts K
que = 4.80 (±0.50) × 104 M−1, K
kae = 4.65 (±0.45) × 104 M−1, and K
del = 9.47 (±0.70) × 104 M−1. The stability of adduct formation is in the order of del>que>kae for tRNA and que>kae>del for DNA. Low flavonoid concentration
induces helical stabilization, whereas high pigment content causes helix opening. A partial B to A-DNA transition occurs at
high drug concentration, while tRNA remains in A-family structure. The antioxidant activity of flavonoids changes in order
delphinidin>quercetin>kaempferol. The results show intercalated flavonoids can make them strong antioxidants to protect DNA
from harmful free radical reactions. 相似文献
2.
The present work deals with the biosorption performance of raw and chemically modified biomass of the brown seaweed Lobophora variegata for removal of Cd(II) and Pb(II) from aqueous solution. The biosorption capacity was significantly altered by pH of the solution
delineating that the higher the pH, the higher the Cd(II) and Pb(II) removal. Kinetic and isotherm experiments were carried
out at the optimal pH 5.0. The metal removal rates were conspicuously rapid wherein 90% of the total sorption occurred within
90 min. Biomass treated with CaCl2 demonstrated the highest potential for the sorption of the metal ions with the maximum uptake capacities i.e. 1.71 and 1.79 mmol g−1 for Cd(II) and Pb(II), respectively. Kinetic data were satisfactorily manifested by a pseudo-second order chemical sorption
process. The process mechanism consisting of both surface adsorption and pore diffusion was found to be complex. The sorption
data have been analyzed and fitted to sorption isotherm of the Freundlich, Langmuir, and Redlich–Peterson models. The regression
coefficient for both Langmuir and Redlich–Peterson isotherms were higher than those secured for Freundlich isotherm implying
that the biosorption system is possibly monolayer coverage of the L. variegata surface by the cadmium and lead ions. FT-IR studies revealed that Cd(II) and Pb(II) binding to L. variegata occurred primarily through biomass carboxyl groups accompanied by momentous interactions of the biomass amino and amide groups.
In this study, we have observed that L. variegata had maximum biosorption capacity for Cd(II) and Pb(II) reported so far for any marine algae.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
3.
Ikonomopoulou MP Bradley AJ Whittier JM Ibrahim K 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(8):775-782
We report for the first time the presence of a sex steroid-binding protein in the plasma of green sea turtles Chelonia mydas, which provides an insight into reproductive status. A high affinity, low capacity sex hormone steroid-binding protein was identified in nesting C. mydas and its thermal profile was established. In nesting C. mydas testosterone and oestradiol bind at 4°C with high affinity (K
a = 1.49 ± 0.09 × 109 M−1; 0.17 ± 0.02 × 107 M−1) and low binding capacity (B
max = 3.24 ± 0.84 × 10−5 M; 0.33 ± 0.06 × 10−4 M). The binding affinity and capacity of testosterone at 23 and 36°C, respectively were similar to those determined at 4°C. However, oestradiol showed no binding activity at 36°C. With competition studies we showed that oestradiol and oestrone do not compete for binding sites. Furthermore, in nesting C. mydas plasma no high-affinity binding was observed for adrenocortical steroids (cortisol and corticosterone) and progesterone. Our results indicate that in nesting C. mydas plasma temperature has a minimal effect on the high-affinity binding of testosterone to sex steroid-binding protein, however, the high affinity binding of oestradiol to sex steroid-binding protein is abolished at a hypothetically high (36°C) sea/ambient/body temperature. This suggests that at high core body temperatures most of the oestradiol becomes biologically available to the tissues rather than remaining bound to a high-affinity carrier. 相似文献
4.
Endogeneous levels of zinc and copper were found to be 1.2±0.1×10−2 and 0.3±0.1×10−2 μg/A260 unit, respectively, in polysomal fractions from control animals; cadmium, however, was undetectable. In experimental
animals (injected with cadmium) zinc, copper, and cadmium were found in polysomal fractions isolated by two different methods.
One hour after a cadmium injection there was a rise in both the zinc and copper content of the polysomal fractions, which
then declined steadily to below control levels by 16 h. Neither zinc nor cadmium were dialyzable from these fractions by a
TRIS buffer; however, addition of 0.01M EDTA to the buffer resulted in removal of 75% of the zinc and all of the detectable cadmium.
The addition of cadmium (CdCl2) to control supernatants (adjusted to the cadmium concentration present in supernatants 6 h after in vivo exposure) resulted
in metal binding to polysomal fractions in levels comparable to those observed after in vivo exposures to the metal. When
cadmium was added in the form of cadmium thionein, a smaller fraction of the metal was isolated with the polysomal fraction.
Cadmium bound to polysomal fractions in vivo (24 h after exposure) was sensitive to release by protease digestion, but insensitive
to release by ribonuclease digestion. 相似文献
5.
Lens Major Intrinsic Protein (MIP) is a member of a family of membrane transport proteins including the Aquaporins and bacterial
glycerol transporters. When expressed in Xenopus oocytes, MIP increased both glycerol permeability and the activity of glycerol kinase. Glycerol permeability (p
Gly
) was 2.3 ± 0.23 × 10−6 cm sec−1 with MIP vs. 0.92 ± 0.086 × 10−6 cm sec−1 in control oocytes. The p
Gly
of MIP was independent of concentration from 5 × 10−5 to 5 × 10−2
m, had a low temperature dependence, and was inhibited approximately 90%, 80% and 50% by 1.0 mm Hg++, 0.2 mm DIDS (diisothiocyanodisulfonic stilbene), and 0.1 mm Cu++, respectively. MIP-enhanced glycerol phosphorylation, resulting in increased incorporation of glycerol into lipids. This
could arise from an increase in the total activity of glycerol kinase, or from an increase in its affinity for glycerol. Based
on methods we present to distinguish these mechanisms, MIP increased the maximum rate of phosphorylation by glycerol kinase
(0.12 ± 0.03 vs. 0.06 ± 0.01 pmol min−1 cell−1) without changing the binding of glycerol to the kinase (K
M
∼ 10 μm).
Received: 23 May 1997/Revised: 4 August 1997 相似文献
6.
Miriam Altstein Tal Gabay Orna Ben-Aziz Shai Daniel Irina Zeltser Chaim Gilon 《Invertebrate neuroscience : IN》1999,4(1):0033-0040
The binding of [3H]tyrosyl-PBAN28-33NH2 to pheromone gland membranes of the moth Heliothis peltigera was investigated. The study describes the development of a pheromone biosynthesis-activating neuropeptide (PBAN) radioreceptor
assay and demonstrates the presence of a putative PBAN binding site on the pheromone gland. It also describes synthesis of
a radioligand and optimization of binding conditions with respect to membrane preparation, number of gland equivalents, kinetics
of ligand binding and composition of the binding solution. Binding was found to be optimal when membranes were freshly prepared
from frozen glands, incubated at a concentration of one gland equivalent per reaction tube in the presence of 10 mM HCO3
− ions. Equilibrium of ligand binding was obtained after 20 min. Presence of other components such as NaCl, KCl or SH reagents
did not have any effect on binding. Binding was found to be saturable, with a Kd of 5.73 ± 1.05 × 10−6 M and a Bmax of 1.85 ± 0.22 nmol/mg protein. Binding was effectively displaced by unlabeled PBAN1-33NH2 and PBAN28-33ΝΗ2 with a Ki of 4.3 ± 1.1 × 10−6 M and 4.9 ± 2.6 × 10−6 M, respectively.
Accepted: 4 February 1999 相似文献
7.
Short-term treatment of potato tuber (Solanum tuberosum L.) discs with CdCl2 changed glutathione reductase (GR) activity depending on cadmium ions concentrations, kind of tuber and time of incubation.
The increase of GR activity at 10 and 100 μmol·dcm−3 of CdCl2 solutions was marked in less resistant tissues of cv. Bintje after 24 hrs, and was slight in more resistant tissues of cv. Bzura after 72 hrs. At 1 mmol·dcm−3 concentration of CdCl2 rapid and total inactivation in both kind of tissues was observed, which disappeared after a few days. However this elevation
was faster in more resistant tissues. These inhibition effects come from the inactivation process of GR by cadmium. The values
of KI for cadmium and KM for GSSG of GR from potato tuber tissues indicated that enzyme from more resistant tissues possessed lower affinity to toxic
metal and higher affinity to substrate. 相似文献
8.
Streptomyces lividans 1326 carries inducible mercury resistance genes on the chromosome, which are arranged in two divergently transcribed operons.
Expression of the genes is negatively regulated by the repressor MerR, which binds in the intercistronic region between the
two operons. The merR gene was expressed in E. coli using a T7 RNA polymerase/promoter expression system, and MerR was purified to around 95% homogeneity by ammonium sulfate
precipitation, gel filtration and affinity chromatography. Gel filtration showed that the native MerR is a dimer with a molecular
mass of 31 kDa. Two DNA binding sites were identified in the intercistronic mer promoter region by footprinting experiments. No evidence for cooperativity in the binding of MerR to the adjacent operator
sequences was observed in gel mobility shift assays. The dissociation constants (KD) for binding of MerR were: binding site I, 8.5 × 10−9 M; binding site II, 1.2 × 10−8 M; and for the complete promoter/operator region 1 × 10−8 M. The half-life of the MerR-DNA complex was 19.4 min and 18.8 min for binding site I and binding site II, respectively.
The KD value for binding of mercury(II)chloride to MerR, again determined by mobility shift assay, was 1.1 × 10−7 M.
Received: 18 August 1998 / Accepted: 5 May 1999 相似文献
9.
Zinc, cadmium, and copper are known to interact in many transport processes, but the mechanism of inhibition is widely debated,
being either competitive or noncompetitive according to the experimental model employed. We investigated the mechanisms of
inhibition of zinc transport by cadmium and copper using renal proximal cells isolated from rabbit kidney. Initial rates of65Zn uptake were assessed after 0.5 min of incubation. The kinetics parameters of zinc uptake obtained at 20°C were a Jmax of 208.0±8.4 pmol· min−1·(mg protein)−1, aK
m of 15.0±1.5 μM and an unsaturable constant of 0.259±0.104 (n=8). Cadmium at 15 μM competitively inhibited zinc uptake. In the presence of 50 μM cadmium, or copper at both 15 and 50 μM, there was evidence of noncompetitive inhibition. These data suggest that zinc and cadmium enter renal proximal cells via
a common, saturable, carrier-mediated process. The mechanisms of the noncompetitive inhibition observed at higher concentrations
of cadmium or with copper require further investigation, but may involve a toxic effect on the cytoskeleton. 相似文献
10.
Chlorogenic acid, 3’-O-caffeoyl D-quinic acid, is an inherent ligand present inHelianthus annuus L. The effect of pH on chlorogenic acid binding to helianthinin suggests that maximum binding occurs at pH 6.0. The protein-polyphenol
complex precipitates as a function of time. The association constant of the binding of chlorogenic acid to helianthinin, determined
by equilibrium dialysis, at 31°C has a value of 3.5 ± 0.1 × 104M−-1 resulting in a ΔG value of − 6.32 ± 0.12 kcal /mol. The association constantK
ais 1.0 ± 0.1 × 104M−1 as determined by ultraviolet difference spectral titration at 25°C with ΔG° of -5.46 ± 0.06 kcal/mol. From fluorescence spectral
titration at 28°C, theK
avalue is 1.38 ± 0.1 × 1 0 4M−1 resulting in a ΔG of − 5.70 ± 0.05 kcal/mol. The total number of binding sites on the protein are 420 ± 50 as calculated
from equilibrium dialysis. Microcalorimetric data of the ligand-protein interaction at 23°C suggests mainly two classes of
binding. The thermal denaturation temperature,T
mof the protein decreases from 76°C to 72°C at 1 × 10−3M chlorogenic acid concentration upon complexation. This suggests that the complexation destabilizes the protein. The effect
of temperature onK
aof chlorogenic acid shows a nonlinear increase from 10.2°C to 45°C. Chemical modification of both lysyl and tryptophanyl residues
of the protein decreases the strength of binding of chlorogenic acid. Lysine, tryptophan and tyrosine of protein are shown
to be present at the binding site. Based on the above data, it is suggested that charge-transfer complexation and entropically
driven hydrophobic interaction are the predominant forces that are responsible for binding of chlorogenic acid to the multisubunit
protein, helianthinin.
Publication No. 324. 相似文献
11.
Herbert R. L. Drouin 《European biophysics journal : EBJ》1999,28(7):600-604
A new ion-selective liquid membrane microelectrode, based on the neutral carrier 1,1′-bis(2,3-naphtho-18-crown-6), is described
that shows the dependence of EMF on the activity of divalent putrescine cations a
Put, with the linear slope s
Put = 26 ± 3 mV/decade (mean ± SD, N = 18), in the range 10−4–10−1 M at 25 ± 1 °C. Values of potentiometric putrescine cation selectivity coefficients of logK
Pot
Put
j
(mean ± SD, N) are obtained by the separate solution method for the ions K+ (1.0 ± 0.4, 10), Na+ (−1.2 ± 0.4, 8), Ca2+ (−2.3 ± 0.5, 10) and Mg2+ (−2.5 ± 0.5, 7). The microelectrode can be applied for the direct analysis of the activities of free divalent putrescine
cations in the range 5 × 10−4 to 10−1 M in an extracellular ionic environment. Established analytical methods, e.g. high performance liquid chromatography, determine
the total concentration of the derivatives of free and bound putrescine.
Received: 20 December 1998 / Revised version: 7 May 1999 / Accepted: 27 May 1999 相似文献
12.
Paolo Ascenzi Alessandro Bolli Alessandra di Masi Grazia R. Tundo Gabriella Fanali Massimo Coletta Mauro Fasano 《Journal of biological inorganic chemistry》2011,16(1):97-108
Human serum heme–albumin (HSA-heme) displays globin-like properties. Here, the allosteric inhibition of ferric heme [heme-Fe(III)]
binding to human serum albumin (HSA) and of ferric HSA–heme [HSA-heme-Fe(III)]-mediated peroxynitrite isomerization by isoniazid
and rifampicin is reported. Moreover, the allosteric inhibition of isoniazid and rifampicin binding to HSA by heme-Fe(III)
has been investigated. Data were obtained at pH 7.2 and 20.0 °C. The affinity of isoniazid and rifampicin for HSA [K
0 = (3.9 ± 0.4) × 10−4 and (1.3 ± 0.1) × 10−5 M, respectively] decreases by about 1 order of magnitude upon heme-Fe(III) binding to HSA [K
h = (4.3 ± 0.4) × 10−3 and (1.2 ± 0.1) × 10−4 M, respectively]. As expected, the heme-Fe(III) affinity for HSA [H
0 = (1.9 ± 0.2) × 10−8 M] decreases by about 1 order of magnitude in the presence of saturating amounts of isoniazid and rifampicin [H
d = (2.1 ± 0.2) × 10−7 M]. In the absence and presence of CO2, the values of the second-order rate constant (l
on) for peroxynitrite isomerization by HSA-heme-Fe(III) are 4.1 × 105 and 4.3 × 105 M−1 s−1, respectively. Moreover, isoniazid and rifampicin inhibit dose-dependently peroxynitrite isomerization by HSA-heme-Fe(III)
in the absence and presence of CO2. Accordingly, isoniazid and rifampicin impair in a dose-dependent fashion the HSA-heme-Fe(III)-based protection of free l-tyrosine against peroxynitrite-mediated nitration. This behavior has been ascribed to the pivotal role of Tyr150, a residue
that either provides a polar environment in Sudlow’s site I (i.e., the binding pocket of isoniazid and rifampicin) or protrudes
into the heme-Fe(III) cleft, depending on ligand binding to Sudlow’s site I or to the FA1 pocket, respectively. These results
highlight the role of drugs in modulating heme-Fe(III) binding to HSA and HSA-heme-Fe(III) reactivity. 相似文献
13.
M. Prado Acosta E. Valdman S. G. F. Leite F. Battaglini S. M. Ruzal 《World journal of microbiology & biotechnology》2005,21(6-7):1157-1163
Summary Biosorption of heavy metals by gram-positive, non-pathogenic and non-toxicogenic Paenibacillus polymyxa P13 was evaluated. Copper was chosen as a model element because it is a pollutant originated from several industries. An
EPS (exopolysaccharide)-producing phenotype exhibited significant Cu(II) biosorption capacity. Under optimal assay conditions
(pH 6 and 25 °C), the adsorption isotherm for Cu(II) in aqueous solutions obeyed the Langmuir model. A high q value (biosorption capacity) was observed with whole cells (qmax=112 mgCu g−1). EPS production was associated with hyperosmotic stress by high salt (1 M NaCl), which led to a significant increase in
the biosorption capacity of whole cells (qmax=150 mgCu g−1). Biosorption capacity for Cu(II) of the purified EPS was investigated. The maximum biosorption value (q) of 1602 mg g−1 observed with purified EPS at 0.1 mg ml−1 was particularly promising for use in field applications. 相似文献
14.
Yada E Nagata H Noguchi Y Kodera Y Nishimura H Inada Y Matsushima A 《Marine biotechnology (New York, N.Y.)》2005,7(5):474-480
An arginine specific protease, Sp-protease, was purified by column chromatography from freeze-dried Spirulina platensis using a five-step process. Purified Sp-protease has a molecular weight of 80 kDa. It hydrolyzed the synthetic substrates
containing arginine residue in the P1 position but did not hydrolyze synthetic substrates containing other amino acid residues,
including lysine residue in the P1 position. Among the synthetic substrates tested, a substrate of plasminogen activator (Pyr-Gly-Arg-MCA)
was hydrolyzed most effectively with the enzyme (Km = 5.5 × 10−6 M), and fibrin gel was solubilized via activation of intrinsic plasminogen to plasmin with the enzyme. Activity was inhibited
completely with camostat mesilate (Ki = 1.1 × 10−8 M) and leupeptin (Ki = 3.9 × 10−8 M) but was not inhibited with Nα-tosyl-L-lysine chloromethyl ketone (TLCK). The optimum pH of the enzyme has a range of pH 9.0 to pH 11.0. The optimum temperature
was 50°C; the enzyme was stable at 0–50°C. 相似文献
15.
In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (E
m) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 μM to 1 mM) for several hours
to one week were studied. The E
m values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization
was concentration-dependent reaching the value of diffusion potential (E
D) when the Cd concentration exceeded 100 μM. The values of E
D ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of E
m was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 μM) or complete
repolarization (Cd < 100 μM) was observed within 8–10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly
after the maximum repolarization of E
m a continuous concentration-dependent decrease of E
m followed at all Cd concentrations. Depolarization of E
m was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 μM to
1 mM Cd, with the exception of root cells treated with 1 and 10 μM Cd for 24 and 48 h. Time course analysis of Cd impact on
root respiration revealed that at higher Cd concentrations (> 50 μM) the respiration gradually declined (∼ 6 h) and then remained
at this lowest level for up to 24 h.
All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher
than 100 μM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible
changes in the electrogenic plasma membrane H+ ATPase because fusicoccin, an H+ ATPase activator diminished the depolarizing effect of Cd on the E
m. The depolarization of E
m in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability,
and activity of H+ ATPase. 相似文献
16.
Bibudhendra Sarkar 《Biological trace element research》1989,21(1):137-144
The binding of Cu(II), Zn(II), Ni(II), and Cd(II) to protein components in serum, placenta, kidney, and urine was investigated
at physiological pH, using radioisotopes as tracers. All the four metals were bound to albumin and other macromolecules in
serum. However, small amounts were also bound to low molecular weight components of the size 1500–10000 daltons. The nature
of the Cu(II)-binding to α-fetoprotein suggests its important role as the Cu(II)-transporting protein in fetal life. Metal
binding to placental components were studied using both rat placenta and isolated human trophoblast cells. Studies of metal
binding targets in kidney resulted in the isolation of a 4000 daltons acidic polypeptide which binds Ni(II) and Cd(II) with
Kapp=1.1×10−5 and 2.3×10−5, respectively. Studies of metal binding substances in urine reveals the major amounts of these metals binding to substances
of molecular weight 500–5000 daltons. Preliminary amino acid analysis suggests these components rich in acidic amino acids,
similar to what has been found with kidney polypeptide. There may be a general role for such compounds in the handling of
metals in the process of excretion. 相似文献
17.
Juozas Kulys Kastis Krikstopaitis Arturas Ziemys 《Journal of biological inorganic chemistry》2000,5(3):333-340
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 ×107 M−1 s−1to 2.6×108 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 pK
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 1.8×105 M−1 s−1 to 2.0×107 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 1.6×108 M−1 s−1 and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×107 M−1 s−1 and 0.29 eV.
Received: 20 September 1999 / Accepted: 24 February 2000 相似文献
18.
Zohra Chikh Nguyêt-Thanh Ha-Duong Geneviève Miquel Jean-Michel El Hage Chahine 《Journal of biological inorganic chemistry》2007,12(1):90-100
The kinetics and thermodynamics of Ga(III) exchange between gallium mononitrilotriacetate and human serum transferrin as well
as those of the interaction between gallium-loaded transferrin and the transferrin receptor 1 were investigated in neutral
media. Gallium is exchanged between the chelate and the C-site of human serum apotransferrin in interaction with bicarbonate
in about 50 s to yield an intermediate complex with an equilibrium constant K
1 = (3.9 ± 1.2) × 10−2, a direct second-order rate constant k
1 = 425 ± 50 M−1 s−1 and a reverse second-order rate constant k
−1 = (1.1 ± 3) × 104 M−1 s−1. The intermediate complex loses a single proton with proton dissociation constant K
1a = 80 ± 40 nM to yield a first kinetic product. This product then undergoes a modification in its conformation which lasts
about 500 s to produce a second kinetic intermediate, which in turn undergoes a final extremely slow (several hours) modification
in its conformation to yield the gallium-saturated transferrin in its final state. The mechanism of gallium uptake differs
from that of iron and does not involve the same transitions in conformation reported during iron uptake. The interaction of
gallium-loaded transferrin with the transferrin receptor occurs in a single very fast kinetic step with a dissociation constant
K
d = 1.10 ± 0.12 μM and a second-order rate constant k
d = (1.15 ± 0.3) × 1010 M−1 s−1. This mechanism is different from that observed with the ferric holotransferrin and suggests that the interaction between
the receptor and gallium-loaded transferrin probably takes place on the helical domain of the receptor which is specific for
the C-site of transferrin and HFE. The relevance of gallium incorporation by the transferrin receptor-mediated iron-acquisition
pathway is discussed. 相似文献
19.
P. O. Vardevanyan A. P. Antonyan G. A. Manukyan A. T. Karapetyan A. K. Shchyolkina O. F. Borisova 《Molecular Biology》2000,34(2):272-276
Isotherms of the EtBr adsorption on native and denatured poly(dA)poly(dT) in the temperature interval 20–70°C were obtained.
The EtBr binding constants and the number of binding sites were determined. The thermodynamic parameters of the EtBr intercalation
complex upon changes of solution temperature 20–48°C were calculated: 1.0·106 M−1≤K≤1.4·106 M−1, free energy ΔG
o=−8.7±0.3 kcal/mol, enthalpy ΔH
o≅0, and entropy ΔS
o=28±0.5 cal/(mol deg). UV melting has shown that the melting temperature (T
m) of EtBr-poly(dA)poly(dT) complexes (μ=0.022,4.16·10−5 M EtBr) increased by 17°C as compared with the ΔT
m of free homopolymer, whereas the half-width of the transition (T
m) is not changed. It was shown for the first time that EtBr forms complexes of two types on single-stranded regions of poly(dA)poly(dT)
denatured at 70°C: strong (K
1=1.7·105 M−1; ΔG
o=−8.10±0.03 kcal/mol) and weak (K
2=2.9·103 M−1; ΔG
o=−6.0±0.3 kcal/mol).The ΔG
o of the strong and weak complexes was independent of the solution ionic strength, 0.0022≤μ≤0.022. A model of EtBr binding
with single-stranded regions of poly(dA)poly(dT) is discussed. 相似文献
20.
González-Reimers E Arnay-de-la-Rosa M Velasco-Vázquez J Galindo-Martín L Santolaria-Fernández F 《Biological trace element research》2005,105(1-3):37-51
This study was performed to determine the levels of lead (Pb) and cadmium (Cd) in 63 bone samples of the prehispanic population
of the island El Hierro, comparing them with the values obtained on 98 prehispanic samples from Tenerife, Fuerteventura, Gran
Canaria, and La Palma, all of them in the Canary Islands, and with eight modern samples who served as controls. Prehispanic
individuals from El Hierro showed the lowest bone Pb values of all the archipelago (0.72±1.01 mg/kg), significantly different
(F=6.9, p<0.001) from the values obtained for the population of other islands such as Tenerife (4.87±5.36 mg/kg) or Fuerteventura (4.45±7.85
mg/kg) and also from those of the modern population (30.53±14.62 mg/kg). On the other hand, bone Cd, although slightly lower
in the ancient population groups, was not significantly different when compared with the modern one. In addition, no differences
were observed in bone Cd among the ancient population of the different islands. Bone lead—but not cadmium—kept an inverse
significant relationship with the distance of the burial site both to south Spain (r=−0.31) and Atlantic Morocco (r=−0.28, p<0.001 in both cases). 相似文献