Biomedical subjects

G B Postnikova

Publications and source records attributed to G B Postnikova.

42 records · Page 3Linked to original sources

PubMedDate not supplied

[Electron transfer in hemoproteins. VIII. Influence of ionic strength on the rate of reduction of ferricytochrome c by oxymyoglobin derivatives, chemically modified at histidine residues].

The influence of chemical modification of His residues in Mb on the rate of redox reaction in system MbO2--Cyt c has been studied at different ionic strengths and pH medium. The products of alkylation of all available His by bromacetate and iodacetamide, CM-Mb and CA-Mb, respectively, and myoglobin, modified by spin label 2,2', 6,6'-tetramethyl-4-bromoacetoxypiperidine-1-oxyl (SL) at His residue A10--Sl (His-A10)--Mb have been studied. It has been shown, that the character of the ionic strength dependence of reaction SL(His-A10)--MbO2 with Cyt c at pH 6.0 ann 7.0 is basically analogues to that, observed for intact protein. It means that only His-GH1 of two His residues, His-A10 and His-GH1, situated in the region of "active contact" of Mg with Cyt c molecule, participates in the interactions, essential for electron transfer. The interaction of the charge of this His with the negatively charged group of Cyt c is necessary, probably for the proper arrangement of other interactions in the active complex, because the deprotonation of His-GHl in the studied pH interval decreases the rate of the process by more than one order of magnitude. The rate of oxidation of MC-MbO2 and CA-MbO2 by ferricytochrome c, in contrast to intact protein, shows a weak dependence on the ionic strength and does not depend on the pH medium, throughout the range of ionic strengths from 0.005 to 1.0. The cause of the radical change in the ionic strength dependence is, probably, nearly entire disturbance of electrostatic interactions in the active complex due to chemical modification of His residues in the site of "active contact", and first of all, the His-CHl residue. The fact, that during alkylation of all available His in Mb the electron transfer persists in the system, points to that in the process of electron transfer to cytochrome c, uncharged group, most probably "inner" His-B5, participates. Based on the data on spatial structure and the obtained results, the positions of the charged groups in the site of "active contact" of Mb with Cyt c molecule are presented.

Animals↗

PubMedDate not supplied

[Electron transport in hemoproteins. VIII. The effect of chemical modification of ferricytochrome C on the rate of its reduction by oxymyoglobin].

The influence of chemical modification of separate amino acid residues in ferricytochrome c (Cyt c) on the rate of the redox reaction with MbO2 has been studied at various pH and ionic strength values. It is shown that alkylation of His-33 and Met-65 by bromacetate does not affect the reaction rate. On the contrary, acylation of Tyr-74 or one of the neighbouring lysines, Lys-72 or Lys-73, by the spin-label N-(2,2',5,5'-tetramethyl-3-carboxypyrrolin-1-oxy)-imidazol diminishes sharply the efficiency of electron transfer in the redox system studied. Besides, unlike the reaction between native proteins, the rate of electron transfer in this case does not depend on ionic strength. The modification of Tyr-74 or Lys 72/43 does not alter the midpoint potential and the entire conformation of Cyt c. The observed effects can therefore be explained by essential disturbance of interactions, first of all, the electrostatic ones in the active complex, which is induced by the attachment of the bulky reagent to the site of "active contact" of Cyt c. Based on the obtained findings and the atomic coordinates of Cyt c, the positions of all charge and some uncharged groups on the surface of Cyt c interacting with myoglobin during electron transfer are presented.

Animals↗

PubMedDate not supplied

[Comparison of the structures of different forms of sperm whale myoglobin in solution using wide angle x-ray scattering].

Experimental X-ray diffuse scattering curves in a wide range of angles for oxy-, deoxy-, met- and cyan-forms of sperm whale myoglobin in solution have been obtained. It has been found that scattering indicatrices of these ligand forms of myoglobin are well compatible with each other and differ from the theoretical scattering curve of met-myoglobin, calculated from the structure of this protein in crystal. The conclusions have been drawn: (1) on the similarity of myoglobin structures in solution for all the protein forms studied; (2) on the difference in the structure of the above ligand forms of myoglobin in solution from the structure of the protein in crystal by a slight shift (about 2 A) of the "hairpin" GH.

Animals↗

PubMedDate not supplied

[Electron transfer in hemoproteins. The applicability of models of electrostatic interaction of molecules for description of the relationship between the myoglobin and cytochrome reaction rate and the ionic strength].

The nonlinear regression method was used for the evaluation of applicability of the known model equations that describe the ionic strength dependence of the rate of reaction between charged molecules to the electron transfer reaction between myoglobin and cytochrome c. The full and simplified equations of Bronsted-Debay-Hukkel and Wherland-Gray equation, as well as equations, derived from models of complementary interactions and "parallel disks" were used. The experimental dependences of reaction rate on ionic strength at all pH values in the pH interval 5-8 have a negative slope which corresponds to opposite charges of reacting particles and does not correspond (even in sign) to the total charges of Mb and Cyt c. It is found that all models considered, except for those of complementary interactions, permit a satisfactory description of the experimental data. In the case of "parallel disks" and Bronsted-Debay-Hukkel equations, however, the optimal values of Z1Z2 and R1 = R2 = R do not correspond to the real size of the Mb-Cyt c electron transfer complex and to the radii and charges at their contact sites found from the experiment. The Wherland-Gray equation allows the best approximation of the experimental ionic strength dependences assuming that Z1Z2 and R1 = R2 = R are some effective parameters that reflect the protein field distribution in the contact site. This distribution can be approximated as a monopole with parameters not coinciding with the parameters of the protein.

Cytochrome c Group↗

PubMedDate not supplied

[Applicability of molecular electrostatic interaction models to describing ionic strength dependence of reaction rate between myoglobin and cytochrome c].

The nonlinear regression method was used for the evaluation of applicability of the known model equations (Wherland-Gray, Brönsted-Debay-Hukkel and "parallel disks") which describe the ionic strength dependence of the reaction rate between charged molecules to the redox reaction of cytochrome c with sperm whale myoglobin modified at His 12(A10) with the bromoacetate spin label, and pig myoglobin. Unlike the native sperm whale Mb studied earlier [1], the objects chosen have monotonous pH-dependence of the reaction rate and are more simple with regards to electrostatic interactions in the electron-transfer complex. This allowed to study the influence of the total as well as the local protein charge on the correspondence of the ion strength dependencies to the theoretical models and optimal parameters of the equations. It was shown that the models considered, as in the case of the native sperm whale Mb-Cyt c reaction, permit satisfactory description of the experimental data, but the obtained parameters cannot be applied to the whole proteins or their contact sites. In the best case (Wherland-Gray equation) it is possible to do if the distribution of electrostatic potential in the contact area is considered. The reason can be that, unlike other protein redox-systems, the contact sites of both Mb and Cyt c have the charged residues of both signs, and the His GH1 residue located in the contact Mb site is not only involved in the electrostatic interactions in electron-transfer complex, but also participates directly in the mechanism of charge transfer.

Animals↗

PubMedDate not supplied

[The myoglobin level in skeletal muscles of the hibernating Iakutiia ground squirrel Citellus undulatus].

Many characteristics of the ground squirrel metmyoglobin (Mb) were found to be similar to those of the pig and different from the whale ones. The Mb content in winter time was 2.5-3.0-fold higher in hibernating and arousing ground squirrels than in alert ones. This seems to be connected with the high demand of oxygen in the muscles at the first stage of arousal.

Animals↗