PubMed Health⌕ Search

Biomedical subjects

G B Postnikova

Publications and source records attributed to G B Postnikova.

At least 19 recordsLinked to original sources
PubMed2001

Mechanism of oxidation of oxymyoglobin by copper ions: comparison of sperm whale, horse, and pig myoglobins.

The influence of Cu2+ concentration, pH, and ionic strength of the solution as well as redox-inactive zinc ions on the rate of oxidation of sperm whale, horse, and pig oxymyoglobins (oxy-Mb) by copper ions has been studied. These myoglobins have homologous spatial structures and equal redox potentials but differ in the number of histidines located on the surface of the proteins. It was shown that oxy-Mb can be oxidized in the presence of Cu2+ through two distinct pathways depending on which histidine binds the reagent and how stable the complex is. A slow pH-dependent catalytic process is observed in the presence of equimolar Cu2+ concentration for sperm whale and horse oxymyoglobins. The curves of pH dependence in both cases are sigmoid with pK(eff) corresponding to the ionization. The process is caused by the strong binding of Cu2+ to His113 and His116, an analogous His residue being absent in pig Mb. In contrast, rapid oxidation of 10-15% of pig oxy-Mb is observed under the same conditions (fast phase), which is not accompanied by catalysis because the reduced copper is apparently not reoxidized. The complexing of Cu2+ with His97 situated near the heme is probably responsible for the fast phase of the reaction. The affinity of His97 for Cu2+ must be significantly lower than those of the "catalytic" His residues since the fast phase does not contribute markedly to the rate of sperm whale and horse oxy-Mb oxidation. Increasing copper concentration does not produce a proportional growth in the oxidation rate of sperm whale and horse oxy-Mbs. Which Cu2+ binding sites of Mb make main contributions to the His reaction rate at different Cu2+/Mb ratios from 0.25 to 10 is discussed.

Animals↗
PubMed1999

Myoglobin content in skeletal muscles of hibernating ground squirrels rises in autumn and winter.

The content of myoglobin (Mb) in skeletal muscles of Arctic Yakutian ground squirrel (Citellus undulatus Pallas) was measured in the active euthermic summer and prehibernating autumn animals as well as in hibernating and awake animals in winter. The myoglobin content in winter, irrespective of the state of the animal, was found to be about three times higher than in summer. The content of myoglobin in autumn was also two-fold increased compared to summer, suggesting that high myoglobin level is necessary for hibernation. Analysis of biochemical data available suggests that the increase in myoglobin content in winter is probably related to a high oxygen demand of muscles at the first stage of arousal (non-shivering thermogenesis) when rectal temperature rises from 0 to 10-12 degrees C. At this stage, the oxygen-dependent processes in muscles proceed under the conditions when peripheral blood flow is blocked and anaerobic glycolysis is switched off.

Animals↗
PubMed1997

Seasonal changes in myoglobin content in muscles of hibernating Yakutian ground squirrels.

Myoglobin content in skeletal muscles of the Yakutian ground squirrel Citellus undulatus was measured during different periods of the annual life cycle: in active animals in summer, and in hibernating and awake animals in winter. It was found that the Mb content in winter, irrespective of the state of the animal (hibernating or awake), is 2.5-3-fold higher than in summer. Analysis of biochemical data available in the literature suggests that the increase in Mb content in winter is most probably related to a high oxygen demand of muscles at the first stage of arousal when the body temperature rises from 0 to 10-12 degrees C (non-shivering thermogenesis or thermoregulatory tonus). At this stage, the oxygen-dependent processes in muscles proceed under conditions of blocked peripheral blood flow and failure of anaerobic glycolysis.

Animals↗
PubMed1996

[Conformation properties of heme-containing proteins using spin labels].

The review briefly summarizes the results of spin-label studies of conformational transitions in monomeric globins (myoglobin, leghemoglobin, erythrocruorin) as well as in another heme-containing protein, cytochrome c, induced by heme ligands and pH. In contrast with integral methods of investigation, for proteins with a known spatial structure the use of the spin-labelling technique makes it possible to obtain information on the conformational behaviour of the isolated parts of the protein structure which, alongside with the results obtained by other physico-chemical methods, allows a conclusion on the nature of conformational movements in the protein during its functioning. The experimental results fit well into the model which represents a Mb-like structure as composed of three independent rigid helical fragments: AE(ABCDE), F and GH, whose reciprocal arrangement is controlled by N- and C-terminal salt bridges. Synchronous displacement of the above fragments relative to one another, which is due either to the ligand attachment and structural changes in the heme complex or to disturbances in ionic interactions at the N- and/or C-end(s) of the structure under effect of pH or allosteric effectors, might serve as a structural basis for homo- and heterotropic regulation in hemoglobin. Similarly, the spin label method allows for tracing and obtaining important information about local conformational events in cytochrome c which in the native protein are associated with a change in pH in the range of 5-13 and are accompanied by the substitution of the heme sixth ligand, Met-80, by Lys-79 (pH 9.3), and then by Tyr-67 (pK 11.1). Local changes in the conformation and dynamic properties of native cytochrome c provide, if necessary, global changes in its structure upon alkaline denaturation. It was found that substitution of the heme protein ligand, Met-80, by the external ligand, cyanide, markedly alters the dynamic properties of the polypeptide chain segment 67-75 adjacent to Met-80.

Hemeproteins↗
PubMed1995

[Study of squirrel myoglobin. Oxidation-reduction reaction between squirrel oxymyoglobin and ferricytochrome c].

Metmyoglobin (met-Mb) of Yakutian ground squirrel (Citellus undulatus) was isolated from skeletal muscles and fractionated using gel and ion-exchange chromatography. An electrophoretically homogeneous major fraction of met-Mb (pI 7.05) was obtained with a 90% yield. The rates of the redox reaction between ground squirrel oxy-Mb and horse and ground squirrel ferri-Cyt c were studied in the pH range of 5-8 at ionic strengths ranging from 0.01 to 1. The experimental results were compared to the earlier obtained data for sperm whale and pig Mbs whose three-dimensional structures and physico-chemical properties are well studied. It was shown that the properties of ground squirrel Mb are very similar to those of pig Mb but differ from those of whale Mb. The amino acid sequences of about 50 Mbs from various mammals as well as from some avian and chordate species (Protein Data Bank) were compared. It was found that rodent myoglobins can be divided into two distinct groups. Myoglobins of animals living in water are identical with those of sperm whale and other cetaceans, while myoglobins of ground rodents closely resemble pig Mb. The number of non-homologous amino acid substitutes in each of the two groups (1-2 positions) is much less compared to all rodent myoglobins (8 positions). The charge structure of the Mb contact site interacting with Cyt c in the course of the electron transfer reaction is strictly conservative for all mammalian Mbs tested in this study (but not for birds and chordates). It is assumed that under certain extreme conditions oxy-Mb can directly interact with cell organelles, such as mitochondria.

Animals↗
PubMed1994

[Chemical modification of myoglobin by isothiocyanate reagents. The effect of modifying the N-terminal amino group on protein conformation].

Sperm whale met-Mb was chemically modified by fluorescein isothiocyanate (FITC) and methylisothiocyanate (MITC) at pH 6.5-7.0. Individual met-Mb derivatives, FITC-Mb and MITC-Mb, modified at the alpha-NH2-group of Val I (NAI), were obtained by ion exchange chromatography with 10 and 30% yields, respectively, and characterised. The His 12 (AI0) residue was found to be additionally thiocarbamylated in MITC-Mb. Large amounts of the remaining intact met-Mb (more than 50%) were isolated in both cases alongside with small fractions of the deeper modified protein. The absorption and CD spectra of met-Mb, FITC-Mb and MITC-Mb in the UV and visible spectral regions, the spectrophotometric titration curves in the Soret band and tryptophanyl fluorescence of the apo- and holomyoglobins in the pH range of 2-13 were investigated. It is shown that modification of the N-end had no influence on the conformation (alpha-helicity) of the polypeptide chain of Mb but caused specific changes in the absorption and CD spectra, pK values of met-hydroxy transition, and the pH-dependent fluorescence of the modified species as compared to the native met-Mb. The data obtained evidence in favour of both the changed local conformation of the N-terminal region and the heme environments in FITC-Mb and MITC-Mb.

Animals↗
PubMed1991

Fluorescence study of the conformational properties of myoglobin structure. 1. pH-dependent changes of tryptophanyl fluorescence in intact and chemically modified sperm whale apomyoglobins.

The pH-dependent fluorescence of intact sperm whale apomyoglobin (apo-Mb) containing two tryptophans at positions 7 and 14, and of apo-Mb derivatives modified on Trp7 by 2-hydroxy-5-nitrobenzyl bromide (Koshland reagent) and o-nitrophenylsulphenyl chloride, has been studied. The fluorescence of apomyoglobins modified at His residues by iodoacetamide and bromoacetate, and at the N-terminal alpha-NH2 group by methylisothiocyanate, has also been investigated. The individual fluorescent properties of both tryptophans and their contributions to the total spectrum of apo-Mb have been resolved within the pH range 2-12.5. The quantum yield of the 'buried' Trp14 (lambda max at 326 nm) is shown to be twofold higher at pH greater than 8.5 than that of the 'exposed' Trp7 (lambda max at 333 nm). At pH 8.5-5.5 the fluorescence of Trp14 diminished approximately twofold due to quenching by the ionized His residue, most probably His119. The quenching is evidently dynamic because the fluorescence lifetime is shown to be linearly proportional to quantum yield in this pH range. The fluorescence of Trp7 practically does not change between pH 5.5 and 10.0 but increases 2.5-3-fold in the pH range 5.5-4.3 while the contribution of Trp14 remains constant. The conformational changes at the N-terminal and in the region adjacent to it, as well as in the whole apo-Mb molecule in acidic, alkaline and neutral pH ranges, are considered. A relationship is revealed between conformational states of the heme crevice and the N-terminal part of apo-Mb.

Animals↗
PubMed1991

Fluorescence study of the conformational properties of myoglobin structure. 2. pH- and ligand-induced conformational changes in ferric- and ferrousmyoglobins.

Tryptophanyl fluorescence of high-spin and low-spin complexes of sperm whale ferric- and ferrousmyoglobins, met-, azide- and cyanomyoglobins and deoxy-, oxy- and carboxymyoglobins has been studied in the pH range 2.5-13. The pH-dependent fluorescence of sperm whale metmyoglobin acylated at the N-terminal alpha-amino group by methylisothiocyanate and of bovine metmyoglobin, which contains invariant Trp7 and Trp14 but lacks Tyr151, have also been examined. Drastic changes in the fluorescence were registered in the acidic and alkaline pH ranges which are due to denaturation of Mb. Fluorescent and CD data indicate that at pH less than 4.5 and pH greater than 11.5 the unique spatial structure of the protein is destroyed whereas the secondary structure and integrity are essentially preserved. In all sperm whale and bovine myoglobins studied a local conformational change in the surroundings of Trp is observed which precedes alkaline denaturation. It seems to be due to deprotonation of lysine residues and breakage of the salt bridges essential for the maintenance of the native conformation of the N-terminal and the adjacent region. The parameters of this conformational transition are found to correlate with the spin state of the heme complex. However, analysis of the fluorescence behaviour of different ligand derivatives of myoglobin in the whole pH range studied enables one to conclude that the exact protein conformation depends not only on the spin state of the Fe atom but, to a greater extent, probably on the chemical nature of the ligand and its interaction with the protein groups in the heme cavity. Local conformational changes induced by the replacement of the sixth ligand or by varying pH seem to involve the same region of contacts between the A helix and GH fragment (or between the AE and GH helical complexes) though the extent of the changes may be different.

Animals↗
PubMed1991

Fluorescence study of the conformational properties of myoglobin structure. 3. pH-dependent changes in porphyrin and tryptophan fluorescence of the complex of sperm whale apomyoglobin with protoporphyrin IX; the role of the porphyrin macrocycle and iron in formation of native myoglobin structure.

The porphyrin and tryptophan fluorescence of sperm whale apomyoglobin complexed with protoporphyrin IX has been studied in the pH range 2-13. It has been shown that the fluorescence and absorption spectra of protoporphyrin incorporated into the heme crevice remain constant in the pH range 5.5-10.8 but change significantly at pH less than 5.5 and pH greater than 10.8, due to the acid and alkaline denaturation, respectively, of the complex accompanied by dissociation of protoporphyrin IX. At the same pH ranges, the quantum yield of tryptophanyl fluorescence increases sharply as a result of removal of protoporphyrin, acting as a quencher, from the complex. Other parameters of tryptophanyl fluorescence (maximum position, halfwidth and spectrum shape) change in the alkaline region as well. In the acidic pH range, these parameters change only at pH less than 4.3, indicating that the Trp surroundings are more stable to denaturation than the heme crevice region. Between pH 5.5 and 10.9, where the complex of apomyoglobin with protoporphyrin IX is in its native state, the main parameters of tryptophan fluorescence remain unchanged except for the ratio I325/I350 which diminishes at pH greater than 9.5. Its alteration precedes the alkaline denaturation of the complex and can be explained by a local conformational change induced by the break of the 'salt bridges' essential for the maintenance of the native Mb structure in the N-terminal region. The fluorescence data obtained for apomyoglobin, myoglobin and the complex between protoporphyrin IX and apomyoglobin enable one to compare their structures and to evaluate the role of the porphyrin macrocycle and the iron atom in the formation of the native myoglobin structure and its functioning.

Animals↗
PubMed1986

[pH-dependent changes in the tryptophan and porphyrin fluorescence of the apomyoglobin complex with protoporphyrin IX and methemoglobin].

The fluorescence of protoporphyrin IX (PPIX) complexed with sperm whale apomyoglobin as well as the tryptophan fluorescence of this complex and of metmyoglobin within the pH range of 3.5-13 was studied. It was shown that an increase in pH from 5.3 to 10.8 does not influence the fluorescence of PPIX in the complex and causes no essential changes in the fluorescence of Trp residues, which occur at more acidic and, correspondingly, alkaline pH values simultaneously with the protein denaturation. This is accompanied by a sharp increase in the quantum yield of tryptophan fluorescence due to dissociation of PPIX from the complex. Similar changes are observed in metMb at pH less than 4.3 and greater than 12 which is concomitant with absorption changes in the Soret band, thus indicating a higher stability of metMb towards the acid and alkaline denaturation as compared to the complex. In both cases, a slight alteration in the shape of the tryptophan fluorescence spectrum is observed, which precedes alkaline denaturation of the Mb molecule and is probably due to changes in the conformation of the N-terminal region caused by the break of the salt bridges stabilizing the native structure of the protein.

Animals↗
PubMed1985

Spin-label study of conformational changes induced by pH and ligands in leghemoglobin from yellow lupine root nodules.

Conformational changes induced by ligands and pH in lupine ferrileghemoglobin selectively modified at Tyr-E16 by the imidazolide spin label has been studied by the method of electron spin resonance in the pH range 6-13. It is shown that in the alkaline pH region the bound spin label registers a local conformational transition which precedes the alkaline denaturation of the protein. In aquamet, cyanide and nicotinate complexes of ferrileghemoglobin this transition occurs with pK 10.5, in acetate and azide complexes with pK 11. In all these ligand derivatives the transition is induced by alteration in the ionization state of one group (delta nH+ approximately equal to 1), most probably, the epsilon-amino group of Lys-GH3. The latter is linked with the Glu-A14 residue and this bond is essential for maintaining the native conformation of leghemoglobin. The ligand-induced conformational changes in the vicinity of the label are small and consist, most likely, in some alteration of the mutual arrangement of the AE and GH helical complexes. No correlation has been revealed between the spin state of the heme iron and the conformation of leghemoglobin in the region under study.

Chemical Phenomena↗
PubMed1983

A spin label study of conformational changes in cytochrome c.

Spin-labeled pig heart cytochromes c singly modified at Met-65, Tyr-74 and at one of the lysine residues, Lys-72 or Lys-73, were investigated by the ESR method under conditions of different ligand and redox states of the heme and at various pH values. Replacement of Met-80 by the external ligand, cyanide, was shown to produce a sharp increase in the mobility of all the three bound labels while reduction of the spin-labeled ferricytochromes c did not cause any marked changes in their ESR spectra. In the pH range 6-13, two conformational transitions in ferricytochrome c were observed which preceded its alkaline denaturation: the first with pK 9.3 registered by the spin label at the Met-65 position, and the second with pK 11.1 registered by the labels bound to Tyr-74 and Lys-72(73). The conformational changes in the 'left-hand part' of ferricytochrome c are most probably induced in both cases by the exchange of internal protein ligands at the sixth coordination site of the heme.

Animals↗
PubMedDate not supplied

[Effect of mitochondria on the redox reaction between oxyhemoglobin and ferricytochrome c].

The effect of mitochondria on the redox reaction between oxymyoglobin (oxy-Mb) and ferricytochrome c was studied. The parameters of this reaction in the absence of mitochondria have been investigated earlier. It is shown that the course of oxidation of oxymyoglobin by cytochrome c in the presence of mitochondria differs from that without mitochondria: no reduced cytochrome c is observed; in addition, the order of this redox reaction and its dependence on pH and ionic strength change. The factors influencing the state of mitochondrial membrane and uncouples enhance markedly the reaction rate. The conclusion was drawn that mitochondria directly participate in the oxymyoglobin-cytochrome c redox reaction. The possibility of this reaction in vivo under extreme conditions and during pathological processes is discussed.

2,4-Dinitrophenol↗