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G B Postnikova

Publications and source records attributed to G B Postnikova.

At least 37 records · Page 2Linked to original sources
PubMedDate not supplied

[Oxidation of sperm whale oxymyoglobin, catalyzed by ferrocyanide ions: kinetics and mechanisms].

Specific catalytic oxidation of sperm whale oxymyoglobin by small amounts of potassium ferri- and ferrocyanide, from 1 to 20% in relation to the protein concentration, was studied. The mechanism of catalysis was shown to involve specific binding of the ferrocyanide anion to the protein. The influence of pH and ionic strength of the medium, the [Fe(CN)6]4- concentration and of chemical modification of Mb histidines by bromoacetate, as well as the effect of the Mb complexing with redox-inactive zinc ion on the rate of reaction was examined. The zinc ion forms a stable complex with His 119(GH1) on the Mb surface at the equimolar Zn2+ concentration. The kinetic scheme of the reaction was analyzed, and the equilibrium and kinetic parameters were obtained. It was first shown that the strong oxidant such as potassium ferricyanide is able to react with the same protein by two distinct mechanisms: (i) a simple outer sphere electron transfer over the heme edge and (ii) electron transfer after the specific binding of [Fe(CN)6]4- to oxyMb in the His 119(GH1) region, thus catalyzing the protein oxidation.

Animals↗
PubMedDate not supplied

[Catalytic effect of ferricyanide on the rate of electron transfer between myoglobin and cytochrome c].

The influence of small amounts of low-molecular electron acceptor, potassium ferricyanide, 1 to 20% relative to the cytohrome c concentration, on the rate of electron transfer in the sperm whale oxymyoglobin--horse heart cytochrome c and deoxymyoglobin--cytochrome c systems (under aerobic and anaerobic conditions, respectively) was studied. At low ionic strength, the redox reaction rate was found to increase proportionally to the concentration of ferricyanide in both redox systems. The effect depends on pH in the pH range 5-8, increasing sharply at pH < 6. It was shown that the enhancing of electron transfer is caused by the complexing of [Fe(CN)6]3- with cytohrome c in the Lys72 region, where one of the two strong binding sites for this anion is determined by NMR. Both the high ionic strength and the chemical modification of Lys72 residue inhibit this effect at low ionic strength, markedly decreasing the rate of reaction with myoglobin. Under the same conditions, the effect of ferricyanide in the reaction of oxy-Mb with yeast cytohrome c, which is isopotential to animal cytochromes c but possesses trimethylated Lys72, was several times smaller. In turn, the chemical modification of His residues in myoglobin and the complexing of zinc ion to His119(GH1) almost completely inhibit electron transfer in the systems. Thus, electron transfer between the proteins must proceed through the formation of the Mb.[Fe(CN)6]3-.Cyt c ternary complex, the contacting sites being localized in the His119(GH1) region of myoglobin and near Lys72 of cytohrome c. The increased electron transfer rate in the presence of [Fe(CN)6]3- can be explained by that its binding near Lys72, firstly, provides better electrostatic interactions in the electron transfer complex and, besides, decreases significantly (about 2-fold) the tunneling distance between the two hemes (two lengths of 1.7 and 1.2 nm instead of one of 2.9 nm).

Acetates↗
PubMedDate not supplied

[Study of electron transport in heme proteins. X. Effect of pH, ionic strength, and zinc ions and the rate of ferricytochrome c reduction by oxymyoglobin from swine heart].

The rate of the redox reaction between porcine MbO2 and ferri-Cyt c at different ionic strengths in the pH range 5-8 has been studied. At low ionic strength (I = 0-0.1) the pH dependence curve was found to have a sigmoid shape with pKeff approximately 5.7, implying the effect of ionization of His-119(GH1) at the "active site" of myoglobin on the kinetics of the process. In this range of ionic strengths the rate of the reaction decreases sharply. The slope of the curve in the coordinates of IgKexp versus square root of I/1 + square root of I varies depending on pH. It is greater at pH less than or equal to 6 and smaller at pH 7.5, which is due to deprotonation of His(GH1). At high ionic strength (I greater than 0.1) the rate of electron transfer is negligible, independent of pH and does not practically change as I increases from 0.1 to 1. It is shown that the local electrostatic interactions play a decisive role in the formation of an efficient electron-transfer complex between Mb and Cyt c. The binding of the zinc ion to His(GH1) was found to inhibit the electron transfer at I = 0.01, similarly to what occurs at a high ionic strength, though the "reactive" charges of the proteins are not screened and the positive charge at His(GH1) is retained. This suggests that His(GH1) is directly involved in the mechanism of electron transfer from Mb to Cyt c. The data obtained are compared with earlier data on the effect of pH, ionic strength and zinc ions on the reaction between MbO2 from sperm whale and Cyt c. To explain the higher efficiency of pig MbO2 as electron donor, the electrostatic and steric properties of both myoglobins have been analyzed.

Animals↗
PubMedDate not supplied

[The oxidation of sperm whale, horse, and pig oxymyoglobins, catalyzed by ferrocyanide ions: kinetics and mechanism].

The influence of pH, ionic strength of the solution, and [Fe(CN)6]4- concentration on the rate of oxidation of sperm whale, horse, and pig oxymyoglobins, which is catalyzed by ferrocyanide ions, was studied. These myoglobins have homologous spatial structures and identical redox potentials but differ by the amount of His residues located on the protein surface. The effect of the MbO2 complexing with redox-inactive Zn2+ ion on the reaction rate was also examined. At the equimolar Zn2+ concentration, zinc ions form a stable complex with His119(GH1). It was found that the kinetic behavior of horse MbO2, which lacks His12(A10) substituted for by Gln, is fully analogous to one of sperm whale MbO2, while the oxidation of pig MbO2, three histidines of which, His12, His113(G14), and His116(G17), are replaced by Gln, is strongly inhibited. The mechanism of the catalysis was shown to involve specific binding of [Fe(CN)6]4- to the protein at the His119(GH1) site, which is in accord with the large positive electrostatic potential of this site and the presence here of a cavity large enough to accommodate [Fe(CN)6]4-. The nearby His113 and His116 residiues, which are absent in pig Mb, also play a very important role in the catalysis, because their protonation (especially of the last residue) is most likely responsible for the week oxidation of bound [Fe(CN)6]4- by dissolved oxygen.

Animals↗
PubMedDate not supplied

[Myoglobin and mitochondria: kinetics of oxymyoglobin deoxygenation in mitochondria suspension].

The kinetics of whale MbO2 deoxygenation was studied spectrophotometrically in the presence of breathing rat mitochondria under conditions when mitochondria were separated from the protein solution by a semipermeable film capable to transfer only low-molecular-weight compounds and directly in the solution of MbO2 with mitochondria (incubation medium: 15-35 mM succinate, 150 mM sucrose, 100 mM KCl, 0.5 mM EGTA, 5 mM KH2PO4, 10 mM MOPS, pH 7.4). It was shown that the splitting of O2 from MbO2 at physiological pO2 is possible only if it directly contacts mitohondria. The deoxygenation rate does not depend on the protein concentration (zero order on [MbO2] as opposite to the first order reaction in the absence of mitochondria) and completely coincides with the rate of oxygen consumption by mitochondria under the same conditions, as indicated by the polarographic data. The dependence of the MbO2 deoxygenation rate on the concentration of mitochondria and the protein, and on the total charge of the MbO2 molecule was studied using horse MbO2 (pI 7.1), sperm whale MbO2 (pI 8.3), its zinc complex, Zn-MbO2 (pI > 8.3), and the sperm whale MbO2 derivative carboxymethylated at His residues, CM-MbO2 (pI 5.2). The mechanism of MbO2 deoxygenation in the cell obviously actuates its interplay with the mitochondrial membrane. As a result, the affinity of Mb to oxygen decreases several times, which corresponds to a shift of the Mb dissociation curve to higher pO2 values.

Animals↗
PubMedDate not supplied

[The mechanism of oxymyoglobin oxidation catalyzed by ferrocyanide ions: chemically modified and mutant sperm whale myoglobins].

A comparative study of the rate of ferrocyanide-catalyzed oxidation of native sperm whale MbO2, its chemically modified derivative in which all accessible His residues are alkylated by sodium bromoacetate, (CM-MbO2), and mutant sperm whale MbO2 with His119 replaced by Asp residiue, [MbO2(His119-->Asp)] was carried out. The influence of pH, ionic strength, and [Fe(CN)6]4- concentration on the oxidation rate was investigated, as well as the effect of complexing MbO2 with redox-inactive Zn2+ ion, which, at the equimolar Zn2+ concentration, forms a stable complex with His119(GH1) on the protein surface. It was shown that the mechanism of the catalysis involves specific binding of [Fe(CN)6]4- to the protein at the His119(GH1) region, which is in agreement with a large positive electrostatic potential and the presence at this site of Mb of a cavity large enough to accommodate [Fe(CN)6]4- anion. The protonation of nearby His113 and His116 residiues (especially of the latter) plays a very important role in the catalysis, promoting the fast oxidation of bound [Fe(CN)6]4- by dissolved oxygen. Only the presence of these both necessary conditions in MbO2 structure provides its effective oxydation catalyzed by ferrocyanide.

Amino Acid Substitution↗
PubMedDate not supplied

[Chemical modification of ferricytochrome c by N-(2,2',5,5'-tetramethyl-3-carboxypyrroline-1-oxyl)-imidazole].

Chemical modification of pig heart ferricytochrome C by the paramagentic analog of N-acetylimidazole-N-(2,2',5,5'-tetramethyl-3-carboxypyrroline-1-oxyl)-imidazole has been studied. Two main modified preparations, both with the single spin label per molecule, have been isolated by means of chromatography on CM-Sephadex C-25. The study of UV-difference spectra of the SL-preparations versus native Cyt C, the spectrophotometric titration of the tyrosine residues in modified proteins and the study of their reaction with hydroxylamine allow to conclude that one of these preparations (fraction II) is lysine modified Cyt C-SL(Lys)-Cyt C and the other (fraction III) is tyrosine modified protein-SL(Tyr)-Cyt C. From the present results and the data available in literature the most probable location of the modification sites in the three-dimentional structure of Cyt C is Tyr-74 in SL (Tyr)-Cyt C and one of the neighbouring lysil residues Lys 72 or Lys 73 in SL (Lys)-Cyt C on the molecular surface. From the absorbtion and CD-spectra of the modified and native Cyt C in the spectral interval 190--450 nm and from the high resolution PMR data the conclusion has been made that the chemical modification does not alter the immediate vicinity of the heme group and the molecular structure of Cyt C as a whole. Therefore both SL-modified preparations might be useful for the conformational and functional investigations of Cyt C.

Cytochrome c Group↗
PubMedDate not supplied

[Electron transport in hemoproteins. IX. The effect of zinc ions on the rate of oxymyoglobin oxidation by ferricytochrome c].

The effect of zink ions, which according to the X-ray data are bound to the His GH1 residue of myoglobin, has been investigated. It is shown that the electron transfer in the system is almost completely inhibited at the equimolar Zn2+ concentration in the pH range 5 to 8. Unlike the reaction between the intact MbO2 and Cyt c, the electron transfer rate in this case does not depend on pH and ionic strength of the solution. Further increase of Zn2+ concentration up to the 20-fold molar excess has no significant effect on the rate of the process. Since the thermodynamic characteristics of the redox reaction between MbO2 and Cyt c are not altered in the presence of Zn2+, the findings obtained can be interpreted as indicating the important role of His GH1 in the formation of productive electron transfer complex.

Animals↗
PubMedDate not supplied

[Mechanism of electron transfer between myoglobin derivatives and ferricytochrome C].

Progress in the studies of the electron transport mechanism in biological systems is greatly hindered by the lack of detailed structural information about the components of these systems. That is why a study of electron transfer between protein molecules with the known spatial organization in model reactions in vitro is of great importance. In this respect the MbO2--Cyt C oxidation-reduction reaction offers unique possibilities. Studies of the effects of pH and ionic strength of the medium on the kinetics of this reaction in combination with chemical modification of single amino acid residues of Mb and Cyt C enabled us to identify those parts of the surface of haemoproteins where the molecules come into "active contact". A variation in the number or/and the arrangement of the charged groups at the "active sites" of the molecules induced by both changing the medium pH and chemical modification of some of these groups lowers markedly the probability of electron transfer in the system (e.g. His GH1 and His A10 in Mb) or blocks it entirely (acylation of Lys 72 (73) or Tyr 74 in Cyt C). Based on the results obtained and on the data of Mb and Cyt C X-ray analysis, the figures of spatial arrangement of the groups at the "active sites" of these molecules are presented.

Amino Acid Sequence↗
PubMedDate not supplied

[Electron transfer to hemoproteins. II. pH-dependence of the reduction rate of ferricytochrome c by oxymyoglobin].

The pH-dependence of the reduction rate of ferricytochrome C by intact and chemically modified oxymyoglobins has been studied. The modification was performed with respect to histidine residues and alpha-aminogroup of N-terminal valine. Two histidine residues of myoglobin, His A10 and His GH1, are shown to take part in the realization of the "active" contact between the molecules in the course of the reaction. The deprotonation of the first residue contributes to the acceleration and that of the second to the reduction of the reaction. The found orientation of the Mb molecules in the "active complex" implies that at any orientation of cytochrome C the distance between the haemes of the both molecules should be more than 30 A. This makes highly probable that a structure-dependent mechanism of electron transfer in the system under study can be proposed.

Binding Sites↗
PubMedDate not supplied

[Use of triplet state exchange disactivation phenomenon for the study of structure and electron conductivity of proteins].

A method for studying protein structure and estimating its electron conducting properties is proposed. The method is based on the kinetic recording of exchange quenching triplet labels and probes phosphorescence by chromophores or paramagnetic centres. It is shown that different types of exchange interactions (spin exchange, exchange energy transfer) between centres with distance R are described approximately by an equation (I = I0 exp-2R/L) where L changes from 0.7 A (absence of electron coupling--system of type I) to 6.5 A (strong electron coupling--system of type II). I (sec-1) corresponds to exchange energy transfer rate constant or exchange integral in the case of spin exchange. Life-times of excited triplet state eosin-isotiocionate labels connected with the terminal NH2-groups of the following preparations were measured by the method of kinetic phosphorescence decay recording: human oxyhemoglobin, methemoglobin, F- and CN-methemoglobin, metmyoglobin, F- and CN-metmyoglobins. The influence of lysozyme of the nitroxyl spin label bound to His-15 group on the phosphorescence spectrum was investigated. The analysis of our and literature data on the exchange interactions between the centres localized on the protein with known structure (hemoglobin, myoglobin, lysozyme, carboangidrase, bacterial ferredoxin) permit us to conclude that in the examined cases the experimental values correspond to model systems of type I and are different from the dependence in systems of type II by 5--15 order. This allows us to use equation (I) for estimation of the distances between the centres on proteins.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

[Electron transfer in hemoproteins. VI. The dependence of the reduction rate of ferricytochrome c by oxymyoglobin on ionic strength].

The rate of the redox-reaction between MbO2 and ferri-Cyt c has been investigated in the pH range 5-8 under different ionic strength of the solution. The influence of various anions-phosphate, chloride, sulfate and acetat on the rate of the reaction were also studied. It has been shown that under the low ionic strength, I less than 0.1, all pH-dependence curves have pronounced maximum near pH 6.0. While the ionic strength values increase in this interval the reaction rate falls markedly, the profile of lg k versus square root of I/1 + square root of I is linear. Under high ionic strength values, I greater than 0.1, the reaction rate in MbO2-Cyt c system is only slightly influenced by increasing salt concentrations and by pH changing. The results obtained support the idea that the local interactions of charged groups in " active sites" of MbO2 and Cyt c play the most important role in the mechanism of electron transfer. On the contrary net charges of the molecules have a negligible effect on the rate of the reaction. Compared to anions Cl-, SO42- and CH3COO- which influence the reaction rate in an analogous way, phosphate ions have essential inhibiting effect. This is most likely explained by the specific bonding of the phosphate ions to Cty c in the immediate vicinity from the site of the "active contact" with Mb molecule.

Animals↗