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Biomedical subjects

I I Stepuro

Publications and source records attributed to I I Stepuro.

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

[Thermal stability and functional properties of human hemoglobin in the presence of aliphatic alcohols].

Differential scanning microcalorimetry was used to study thermal stability of the ferro- and ferriforms of hemoglobin at pH 7.4 in phosphate buffer and in buffer mixtures of methanol, ethanol, 1-propanol. Denaturation of the human hemoglobin molecule composed of four subunits was cooperative transition. The thermostability of the hemoglobin forms decreased in the order of carboxyhemoglobin (TD = 82.0 degrees C) > oxyhemoglobin (71.0 degrees C) > methemoglobin (67.0 degrees C). The aliphatic alcohols as cosolvents decreased the hemoglobin stability because of loosening the structure of the globin moiety by disturbing its hydrophobic contacts and hydrogen bonds. These alcohols reduced the oxygen affinity for hemoglobin probably due to perturbation of the R<-->T equilibrium by the decreased bulk dielectric constant of the solvent. Oxyhemoglobin and methemoglobin was converted to hemichrome by high alcohol concentrations.

1-Propanol↗
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[Autooxidation and oxygenation of human hemoglobin].

The processes of reversible oxygen binding and nonreversible autoxidation of human hemoglobin were studied. The activation energy of the oxygen binding, as determined by the temperature dependence of the P50 parameter, was 26 +/- 4 kJ/mol, the activation energy of the autoxidation, as determined by the temperature dependence of the apparent rate constant of autoxidation, was 120 +/- 15 kJ/mol. Pyridoxal phosphate decreased the oxygen affinity of hemoglobin, slightly diminished the cooperativity of the oxygenation process and unaffected the activation energy of the oxygen binding. Pyridoxal phosphate slightly reduced the Bohr coefficient value from 0.70 to 0.65. Pyridoxal phosphate, but not pyridoxal, raised the apparent rate constant of autoxidation reaction. The rate of autoxidation significantly increased as the pH value of the medium decreased, reflecting, probably, protonation of the distal histidine of the hemoglobin. The activation energy of autoxidation was independent of pH. Aliphatic alcohols also increased the rate of the autoxidation process, probably, either by stabilization of the hemoglobin T-state, or by direct nucleophilic displacement of the oxygen molecule.

Hemoglobins↗
PubMedDate not supplied

[Ultrasound induced the formation of nitric oxide and nitrosonium ions in water and aqueous solutions].

Nitric oxide, nitrosonium ions, nitrites, and nitrates are formed in water saturated with air under the action of ultrasound. Nitrosonium ions react with water and hydrogen peroxide to form nitrites and nitrates in sonicated solution, correspondingly. Nitric oxide is practically completely released from sonicated water into the atmosphere and reacts with air oxygen, forming NOx compounds. The oxidation of nitric oxide in aqueous medium by hydroxyl radicals and dissolved oxygen is a minor route of the formation of nitrites and nitrates in ultrasonic field.

Air↗
PubMedDate not supplied

[The effect of temperature on lysis of human erythrocytes by palmitic acid].

An analysis of kinetic curves of erythrocyte hemolysis induced by palmitic acid has shown the existence of some stages of this process. The activation energy of hemolysis, as determined by the temperature dependence of the hemolysis rate constant, was 210 +/- 30 kJ/mol. It was shown by the method of stepwise thermoinactivation of erythrocytes proteins that at temperature of 49 degrees C which corresponded to the framework protein spectrin denaturation temperature, the erythrocyte membrane stability sharply decreased. On the contrary, changes of the cell shape induced by the hyperosmotic medium (0.5 M sucrose) inhibited the palmitic acid-induced erythrocytes hemolysis.

Erythrocyte Membrane↗
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[Mechanical lysis of human erythrocytes. Membrane stabilization by plasma proteins].

Mechanical properties of erythrocyte membranes play an important role in red cell functions. Stability of human erythrocytes under deforming mechanical tensions which occur in the rapidly moving fluid is studied. The activation energy of the mechanical hemolysis determined by the temperature dependence of the hemolysis rate is 55 + 7 kJ/mol. The fragility of erythrocytes rises sharply as the salt concentrations increase. Glutaric dialdehyde forms a certain number of interprotein bonds which increase the fragility of erythrocytes. The mechanical stability of the erythrocyte membrane falls at high (0.5 M) ethanol concentrations. Blood plasma proteins, particularly human serum albumin, have a pronounced stabilizing effect. The hemolysis occurring during the rapid mixing is not probably associated with an osmotic mechanism since high sucrose concentrations do not prevent this process. The mechanical hemolysis depends both on the deforming tension arising in the membrane and on the state of the erythrocyte membrane.

Biomechanical Phenomena↗
PubMedDate not supplied

[Study of heat denaturation of human serum albumin in water-alcohol and water-salt solutions in the presence of organic ligands].

The method of differential scanning microcalorimetry was used to show a decrease in heat stability of serum albumin in the presence of aliphatic alcohols. In aqueous-alcohol media, the melting temperature, denaturation transition enthalpy were decreased, and the protein intermolecular aggregation enhanced. When the alcohol concentration in aqueous solution was elevated, the number of epsilon-amino groups of lysine residues in human serum albumin exposed to the solvent rose from 6-7 in aqueous solution to maximum 20 groups in the aqueous-alcohol solution, respectively. The elevation of ionic strength also induced an increase in the number of exposed lysine residues and was accompanied by an enhancement of protein aggregation. The modification of six amino groups by pyridoxal phosphate or three by glucose in the initial albumin stabilized the protein incubated at 65 degrees-70 degrees C both in the aqueous-alcohol media. At the given concentration and temperature the native protein was denatured and fully aggregated. Aliphatic alcohols displaced fatty acids from the binding sites on the molecule of serum albumin, which resulted in a change in the number of peaks of the melting curve.

Alcohols↗
PubMedDate not supplied

[Features of thiamine diphosphate-dependent enzyme inhibition by oxodihydrothiochrome and its phosphorylated derivatives].

Anticoenzyme action of new derivatives of thiamine: oxodihydrothiochrome and its mono- and diphosphoric esters has been studied in the experiments on mice. It is shown that the given compounds exert an inhibiting action on transketolase and pyruvate dehydrogenase and do not change activity of 2-oxoglutarate dehydrogenase in the animal organism. Antivitamin effect of the studied inhibitors is observed with the lower doses and in the earlier terms as compared with the other known inhibitors of thiamine-diphosphate-dependent enzymes. The preparations inhibit activity of the yeast pyruvate-decarboxylase by the mixed (with respect to thiamine-diphosphate) type (Ki for oxodihydrothiochrome and its mono- and diphosphoric esters: 2.3 x 10(-3), 7.2 x 10(-4), 5.6 x 10(-5) M, respectively). Possible mechanisms of the action of the mentioned compounds as thiamine antimetabolites are discussed.

Animals↗
PubMedDate not supplied

[Various enzymatic and nonenzymatic pathways of acetaldehyde transformation].

In blood acetaldehyde is bound to hemoglobin and serum albumin and interacts with low-molecular-weight components--cysteine, glutathione. The association constants for human serum albumin and human hemoglobin are about 30 M-1 and 410 M-1, respectively. The SH-groups of hemoglobin play an essential role in the interaction of protein with acetaldehyde. The reversible complexes of acetaldehyde with proteins can transform into stable adducts after long incubation with albumin, some other blood proteins but not with immunoglobulins. Acetaldehyde participates as a substrate in the reaction of acetoin formation in homogenates of different tissues. The rate of acetoin formation is about 15 +/- 3 mmol/min per 1 gram of the tissue and essentially increases in the presence of pyruvate.

Acetaldehyde↗
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[Distribution of pyridoxal-5-phosphate between proteins and low molecular weight components of plasma: effect of acetaldehyde].

It is found that approximately 65-70% of pyridoxal-P at physiological concentrations is bound to plasma proteins; 15% of its amount is bound to amino acids and peptides as a result of the Schiff base formation. Over 85% of pyridoxal-P associated with plasma proteins is bound to serum albumin. Inorganic phosphate and NaCl decrease the affinity of pyridoxal-P for albumin or other proteins. Acetaldehyde interacts with the alpha-amino group of the aspartic acid residue of the N-end of the polypeptide chain of the albumin molecule and with two epsilon-amino groups of the lysine residues having anomalously low value of pKa and deprotonated at physiological values of pH of the medium. Acetaldehyde competes with pyridoxal-P for the first (of the highest affinity) binding site of the coenzyme on serum albumin. Acetaldehyde is not bound at the second site of high affinity for pyridoxal-P on serum albumin.

Acetaldehyde↗
PubMedDate not supplied

[Adducts of glycosylated serum albumin with amino acids].

Glycosylation of human serum albumin was conducted by its long incubation with the excess either of D-glucose or D-glucose-6-phosphate at 37 degrees C. The glycosylated fractions were isolated by the cation-exchange chromatography on CM-cellulose. The quantity of glucose bound covalently with protein was determined by thiobarbituric acid. The glucose-modified human serum albumin forms stable adducts with amino acids. These complexes are, evidently, produced as a result of the Schiff's base formation between the carbonyl group of the ketoamine adduct of glucose with protein and primary amino group of amino acid further followed by the Amadori rearrangement.

Amino Acids↗
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[Study of the interaction of pyridoxal-5'-phosphate and human serum albumin in the presence of copper ions by circular dichroism].

When pyridoxal-5'-phosphate (PLP) binds with human serum albumin (HSA) in the molar ratio of 1:1, negative in sign induced Cotton effect is observed in the ligand absorption band. This high affinity center is localized in the second domain at an alpha-helical site of the protein molecule. As a result of adding Cu2+ equimolar concentration a new optically active PLP binding site with the positive sign of Cotton effect is acidic medium and the opposite one in alkaline medium is formed on Lys-4 at the beginning of the polypeptide chain. Inversion of the CD spectrum occurs over the same range of pH of the medium as the change in symmetry of electric field surroundings (rhombic in equilibrium axial) of the copper ion within the equimolar ternary complex HSA: PLP: Cu2+.

Binding Sites↗
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[Complexes of Cu2+ with pyridoxal-5'-phosphate and human and bovine serum albumin].

The copper ion Cu2+ bound to serum albumin in the most strong center stabilizes aldimine bonds formed by PLP with epsilon-NH2 group of 4-Lys and alpha-NH2 1-Asp. The stoichometric ratio of the ternary albumin-PLP-Cu2+ complex is 1:2:1. The imidazole rings of histidine residues are involved in binding of copper ions in the first, second, third centers of the albumin molecule. In this case copper ions increase the binding of PLP with the protein stabilizing Schiff bases produced by epsilon-NH2 group of lysine and PLP. The cooper ion bound to serum albumin in the most strong center forms two types of complexes: with rhombic environment in neutral and alkaline media and axial one at pH less than 5,0. On formation of the ternary complex with PLP the rhombic environment is changed to axial.

Animals↗
PubMedDate not supplied

[Mechanism of interaction of pyridoxal-5-phosphate with human serum albumin].

Four and five molecules of pyridoxal-5-phosphate are irreversibly bound to human serum albumin in neutral aqueous or aqueous-spirituous media, respectively. The first step is a reversible formation of the Schiff bases with lysine residues. It is followed by an irreversible interaction of aldimine bond with an imidazole ring of the neighbouring histidine to form cyclic compounds of substituted aldimine type. Cyclic products of the reaction are characterized by absorption spectra with a maximum at 330 nm and fluorescence spectra with a maximum at 400-410 nm in a neutral medium.

Amino Acid Sequence↗
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[Interaction of acetaldehyde with bovine serum albumin].

At pH 6.8-7.4 acetaldehyde interacts with six primary amino groups of bovine serum albumin to form the Schiff base. Four groups after long incubation most probably interact with imidazole rings of neighbouring hystidine residues to yield cyclic products of substituted aldimines type. The reaction of condensation is described satisfactorily by the second-order equation with the rate constant of 4.5 . 10(-4) M-1 s-1.

Acetaldehyde↗
PubMedDate not supplied

[The visible light-photosensitized binding of pyridoxal-5'-phosphate with bovine serum albumin].

Schiff bases condensible at pH 7.0-10 after prolonged incubation with neighbouring histidine residues to yield cyclic compounds absorbing at 330 nm are formed by means of four molecules of pyridoxal-5'-phosphate (PLP) interacting with epsilon-NH2 groups of lysine in bovine serum albumin. The condensation is accelerated in the light. The number of PLP molecules interacting with imidazole rings of histidine in protein remains invariable in alkaline medium, in 6-8 M guanidine. At pH 4.0-4.5 (N-F transition) one more lysine residue neighboring to histidine becomes exposed. The splitting of histidine imidazole ring by diethylpyrocarbonate, photoxidation by singlet oxygen stop the formation of the PLP cyclic compounds with protein.

Animals↗