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Biomedical subjects

N F Sepetov

Publications and source records attributed to N F Sepetov.

33 records · Page 2Linked to original sources
PubMed1986

[Study of peptide degradation in the serum by 1H-NMR].

Enzymatic degradation of hexapeptide Tyr-D-Ala-Gly-Phe-Leu-Arg in human serum has been investigated by 1H-NMR spectroscopy, and its pathways are suggested. Its final degradation products, tetra- and pentapeptide, are shown to be stable in human serum for several hours. The NMR spectroscopy application for pharmacokinetic studies is substantiated.

Enkephalin, Leucine↗
PubMed1985

A comparative study of structural properties of fibronectin and its 180 kDa fragment.

Fibronectin from human plasma and its 180 kDa fragment which retained collagen-binding, cell-attachment and heparin-binding activities, were studied by velocity centrifugation and 1H-NMR methods. The fibronectin hydrodynamic radius strongly increased at pH 11 while the hydrodynamic properties of the fragment did not change noticeably. 1H-NMR spectroscopy also showed differences in the molecular properties of fibronectin and its 180 kDa fragment. Under physiological conditions the structure of fibronectin differs from that of its 180 kDa fragment. At pH 11 and in 4 M urea no differences in their structures are observed. It is suggested that interdomain and intersubunit interactions play an important role in maintaining the native conformation of intact fibronectin.

Cell Adhesion↗
PubMed1981

[Localization of gramicidin S on the cytoplasmic membrane of Bacillus brevis and its effect on the activity of membrane enzymes].

It was shown that malate dehydrogenase of isolated membranes of the gramicidin S producer Bacillus brevis var. G.-B. (R.-form) is completely inhibited by the antibiotic (approximately 200 mkg/mg of protein). Succinate and NADH dehydrogenases at concentration up to 1 mg per mg of protein are insensitive to it, while corresponding oxidases are inhibited by the antibiotic not more than by 65 -- 75% apparently due to partial damage of the terminal parts of the respiratory chain. The respiration of the producer intact cells is inhibited by exogenous gramicidin S by not more than 55 -- 60%, while the respiration of antibiotic-sensitive cells of M.lysodeikticus is inhibited completely. It was shown that phosphatidyl ethanolamine (50%), phosphatidyl glycerol (15% and diphosphatidyl glycerol (25%) are the major phospholipid components of the membranes of the given strain of Bac. brevis. It was assumed that the resistance of Bac. brevis cells to gramicidin S is partly due to the constant ratio of the charged and amphoteric phospholipids. Using 31P-NMR spectroscopy, the kinetics of free phosphoric compounds in the cells and cell extracts of Bac. brevis during culture growth and gramicidin S synthesis were studied. The content of carbohydrate monophosphate, remained unaffected, while that of nucleoside di- and triphosphates and dinucleotides was low and at definite density and gramicidin S content (above 100 mkg/ml) fell down below the resolution capacity of the method employed. Evidence for gramicidin S localization of the Bac. brevis membrane and possible causes for the manifestation of the NADH dehydrogenase activity at a certain stage of culture growth are discussed.

Bacillus↗
PubMed1980

[Localization of polyphosphates in cells of microorganisms using 31-P-NMR-145, 75 MHz of high resolution].

Using the method of 31P-NMR of high resolution at 145,78 MHz the presence of mobile inorganic polyphosphates in the cells of actinomycetes (Mycobacterium smegmatis), yeasts (Candida albicans and Endomyces magnusii) and bacteria (E. coli) was established. A considerable increase in the intensity and a low field shift of the polyphosphate signal after addition of EDTA to the M. Smegmatis cells can be indicative of possible localization of inorganic polyphosphates in the periplasmic space. The lack of effect of exogenous EDTA and Mn2+ on the polyphosphate signal in the spectrum of E. magnusii cells is probably due to localization of polyphosphates inside the cells. A comparison of 31P-NMR spectra of living cells and bacterial extracts of Staphylococcus aureus, Micrococcus lysodeikticus, Bacillus antracoides, B. megaterium and Salmonella typhimurium is given.

Ascomycota↗
PubMedDate not supplied

Rearrangement, racemization and decomposition of peptides in aqueous solution.

We reported earlier that peptides containing glycine as the third amino acid from the amino end undergo sequence rearrangement of the first two amino acid residues. In the course of this experimental verification of the suggested reaction mechanism, we found extensive racemization of the amino acid residue in position 1. Racemization is preferred over rearrangement in peptides containing amino acids different from glycine in position 3. We demonstrate that this reaction can be used for the selective labeling of peptides. Using model peptides, we suggest a mechanism that explains both the rearrangement and racemization of these peptides in aqueous solution. This mechanism is based on formation of a diketopiperazine-like (DKP-like) structure by attack of the N-terminal amino group on the amide carbonyl group of the second residue in the peptide chain. This tetrahedral intermediate, which contains a secondary amino group derived from the amide bond between the second and third amino acid residue, can (i) decompose with the formation of diketopiperazine and a shortened peptide sequence; (ii) form a bicyclic structure by transanular attack on the first amino acid carbonyl group in the DKP-like ring by the newly formed amino group, leading to the rearranged product; and (iii) form a bicyclic structure by transanular attack of the newly formed hydroxyl group on the carbonyl group in the DKP-like ring, leading to the race-mixed product.

Amino Acid Sequence↗
PubMedDate not supplied

[Effect of linoleic acid and products of its free radical oxidation on succinate dehydrogenase].

Effects of linoleic acid and its oxidation products (with 75--80% content of hydroperoxide) on isolated succinate dehydrogenase were studied by means of spectrophotometry and ESR-spectroscopy. It was shown that unlike the unoxidized acid, low concentrations of its oxidation products increased catalytic activity, while its high concentrations of its oxidation products increased catalytic activity, while its high concentrations brought about a decrease of SH-group content and the amplitude of ESR signal of reduced nonheme iron in the enzyme.

Binding Sites↗
PubMedDate not supplied

[Spatial structure of the cro-repressor in a solution. I. Identification of interaction in a hydrophobic cluster using the nuclear Overhauser effect].

The structure of a bacteriophage lambda cro repressor hydrophobic globule was studied by the technique of 1H NMR spectroscopy at 500 MHz. The analysis of NOE difference spectra and building of the molecular models for the most probable fragments of the secondary structure allowed us to assign many signals in the protein spectrum and to identify the intramolecular interactions which stabilized the hydrophobic globule and the tertiary structure of the molecule. The results suggest that the structure of the cro repressor hydrophobic globule in solution coincides with the crystal one, although there are some differences in the mutual arrangement of the alpha 1 helix and the three-fold beta-sheet. Resonance assignment has made it possible to study conformational changes and specific interactions of the cro repressor by using suitable reporter groups.

Bacteriophage lambda↗
PubMedDate not supplied

[1H-NMR study of protein L7/L12 from bacterial ribosomes].

The 500 MHz 1H-NMR spectra of dimeric protein L12 from ribosomes shows a limited number of unusually sharp signals at room temperature. This is interpreted as evidence for substantial segmental flexibility of the region in the protein molecule. We have analysed the extent of the flexible region and also the size of the organized structures of the molecule. Thus residues 37-50 were found to be highly mobile whereas the N-terminal and C-terminal region are organized into folded domains.

Amino Acid Sequence↗
PubMedDate not supplied

[Study of nucleotide biosynthesis by cultured Brevibacterium ammoniagenes using P31 nuclear magnetic resonance spectroscopy].

Using P31 nuclear magnetic resonance, transformations of phosphorous compounds by the culture Brevibacterium ammoniagenes ATCC 6872 in the course of fermentation aimed at the synthesis of nicotinamide adenine dinucleotide were investigated. It was found that the NAD synthesis by the cells treated with surface active substances was markedly influenced by the presence of a small (initial) ATP quantity and was unaffected by an addition of the synthetic polyphosphate (n-40). It was demonstrated that the cells which were not treated with surface active substances contained orthophosphate, carbohydrate monophosphates, and minor quantities of nucleoside triphosphates, polyphosphates, mono- and dinucleotides. After treatment with surface active substances the cells lost these compounds. It is suggested that polyphosphates of the cell and adenosine monophosphate synthesized during its autolysis may enhance the recovery of the ATP level required to trigger glycolysis which serves as the major producer of ATP in the absence of oxidative phosphorylation.

Adenosine Triphosphate↗