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Biomedical subjects

A N Nekrasov

Publications and source records attributed to A N Nekrasov.

18 recordsLinked to original sources
PubMed2001

A numerical measure of amino acid residues similarity based on the analysis of their surroundings in natural protein sequences.

A measure of similarity between amino acid residues based on the analysis of the surroundings of each residue in primary structures of native proteins is proposed. The statistical data used for this purpose were obtained from the analysis of 168,808 protein sequences, which comprise the Protein Identification Research database (release 63). Using various threshold values of the proposed measure, amino acid residues were classified into several groups. The classification elaborated differs essentially from groupings previously used. The numerical measure of amino acid residues similarity can be used in site-directed mutagenesis studies for the prediction of probability of local spatial rearrangements in proteins.

Amino Acid Sequence↗
PubMed1997

Modeling of in vivo proteolytic degradation of hemoglobin.

Based on the amino acid sequences of endogenous peptides and X-ray spatial structure, mechanism of the in vivo proteolly degradation of bovine hemoglobin was analysed. The degradation was shown to be a multi-stage process. Its first stage is determined by the spatial organization of the native protein substrate, and the next stages-by the distribution of the electrostatic field potential of the protein fragments formed at the earlier stage.

Amino Acid Sequence↗
PubMed1996

Cyclo(-GLY-DSIP), A cyclic analog of the delta-sleep-inducing peptide: computer simulation of spatial structure involving NMR data.

The spatial structure of cyclo(-Gly-DSIP-), a physiologically active analog of the delta sleep-inducing peptide, was determined by computer modelling using 1H NMR data. An interesting feature of the spatial structure in DMSO was detected. One side of almost planar resulting conformation is formed by the side chains of the Asp5, Ser7 and Glu9 residues, the side chain of the Trp1 residue forming the other part of the outer surface. This feature may be associated with the functional properties of the peptide.

Amino Acid Sequence↗
PubMed1995

The features of the spatial structure of the gramicidine A-cesium complex.

Earlier obtained two-dimensional 1H-NMR spectroscopy data were used to analyze the spatial structure and conformational mobility of the double right increases decreases pi pi 7.2 LD helix of the complex formed by gramicidine A and Cs+ ions in an organic solvent (a chloroform-methanol mixture). Analysis of the experimental data permitted the determination of a set of conformations for each of the high-mobility residue side chains in the solution. The energy refinement of the most probable conformation of the double right increases decreases pi pi 7.2 LD helix was made and conformational rearrangements of the tryptophan residue side chain were studied in detail.

Cesium↗
PubMed1993

[The effect of spaced hypobaric hypoxia on the maximal hydraulic conductivity of the vascular bed, the supply of capillaries to and the size of the muscles fibers in rats].

6-7-month-old male Wistar rast were divided into three groups. On group of rats remained intact and lived under normal conditions (Group 1; n = 12). Groups 2 (n = 12) and 3 (n = 14) were exposed in hypobaric chamber (18-20 h a day and 2 h a day, respectively) for 2 weeks. The partial O2 pressure was maintained equivalent to 5000 m altitude. The hypoxia produced decreases of structural vascular resistance in hindquarters in Group 2 by 20-25% and in Group 3 by 17-20% (p < 0.05) under all perfusion pressure values. No significant changes in capillary density, capillary per fibre ratio in m. extensor hallucis proprius were found in rats exposed to hypobaric hypoxia for both durations. The cross-sectional area type I fibres (but not II fibres) (CSA) in Group 2 was significantly (p < 0.05) decreased (611 +/- 44 microns 2 vs 779 +/- 49 microns 2 in controls), continuous hypoxia produces significant reduction in type I fibre diffusion distances.

Animals↗
PubMed1993

[Effect of training on the structural-metabolic indicators in athletes' skeletal muscles].

Muscle biopsy samples were taken from m.vastus lateralis of ski-runners during the training season and 4 months after training (consisting presumably of aerobic exercises). Metabolic enzyme activities, fiber cross-sectional areas, capillary supply indices and parameters of oxygen uptake by intact mitochondria in skinned fibers were measured. Training did not induce any appreciable changes in the NADH-tetrazolium reductase activity, maximal oxygen uptake by mitochondria, mean fiber size or capillary density. At the same time, there were significant increases in the cytochrome c oxidase activity, respiratory control index and creatine-stimulated respiratory rate. The activities of alpha-glycerophosphate dehydrogenase, malate dehydrogenase and myoglobin peroxidase as well as the basal respiratory rate of mitochondria decreased as a result of training. The data obtained testify to the possibility of qualitative adaptations in the respiratory chain of mitochondria.

Adolescent↗
PubMed1991

Comparison of the predictive abilities of different methods based on information theory: searching for receptor-binding sites.

A comparison of a new method of searching for functionally important sites in proteins and peptide hormones with a previously published method is presented. All methods are based on information theory that holds that rare oligomers contain much information and, thus, are likely to be important for specific functional activity. Twenty-five proteins and peptide hormones with known receptor-binding sites were studied; the new method showed good predictive ability. However, taking into account short-range sequential preferences in protein structures, the predictive ability of methods based on information theory, at least for the receptor-binding site predictions, was not greatly improved.

Algorithms↗
PubMed1991

[The characteristics of the skeletal muscle fibers of the m. vastus lateralis in highly qualified skaters (a morphometric analysis)].

Morphometrical characteristics of the skeletal muscle fibers of the m. vastus lateralis has been presented in the skaters of a high qualification. The muscle biopsies have been obtained by means of the needle biopsy method from 5 sprinters and 10 classical all-round competitors. Longitudinal sections of the peripheral and central parts of the muscle fiber have been investigated, subdividing the fibers in accordance with certain ultrastructural criteria into two types: slow and fast. The area of mitochondria, myofibrils, lipid inclusions has been determined by means of the system of the image analysis ACM-68K (Leitz, BRD). To the defining factors in the skater muscle ultrastructure, influencing the level of sporting achievements, a high parameter of the volumetric density of the whole mitochondrial population (7.6% in the sprinters and 9.2% in the all-around competitors) and an exceptionally high parameter of the sarcoplasmic density (28.5% in the sprinters and 36% in the all-around competitors) should be ascribed. The morphometrical data of the skaters muscle fiber are compared with the muscle parameters (according to the literature data) of the m. vastus lateralis in high qualification sportsmen of other specialization and in nontrained persons.

Biopsy, Needle↗
PubMed1988

[Analysis of the composition of skeletal muscle fibers in skaters' muscles].

Muscle fibers composition was investigated in vastus lateralis muscles of 103 skaters. In the total population of skaters muscle fibers composition was as follows: muscle fibers, type I--in 54 +/- 2%, muscle fibers, type II A--in 35 +/- 1% and muscle fibers, type II B--in 11 +/- 1%. 13 +/- 8% muscle fibers, type I; 1.56 +/- 6% muscle fibers, type II A and 31 +/- 7% muscle fibers, type II B were observed in the muscles of sprinters, while the muscles of long-distance skaters contained 60 +/- 4%, 33 +/- 4% and 7 +/- 2% muscle fibers, respectively.

Adenosine Triphosphatases↗
PubMedDate not supplied

[The morphological adaptation of the fibers of the human m. triceps surae during local endurance training].

Under investigation were effects of local endurance training of triceps of the calf in physically active volunteers who performed plantar bending in the talocrural articulation 3-4 times a week for 8 weeks with 30% of the maximum arbitrary effort for 40 minutes with 60 movements a minute. The exercise was fulfilled by one foot only. The local training resulted in a 19% greater density of capillaries in the triceps of the calf and in 30% greater amount of capillaries per a fiber. No significant changes were found during training in the ratio of the I and II types of fibers and in their area of cross section, although a tendency for hypertrophy of the Ist type fibers was noticed. Changes in the cross section area of the Ist type fibers and capillary density during training had a considerable negative interrelation. These findings show that the character of the muscle response to training is determined by a correlation of the parameters characterizing its initial state and the parameters of the morphological optimum, corresponding to the given level of functional activity.

Adaptation, Physiological↗
PubMedDate not supplied

[Ultrastructural changes in the skeletal muscles during local endurance training (a morphometric study)].

Biopsies of m. triceps surae were studied in physically active students-volunteers. Flexion of the foot sole 40 minutes in duration with 30% maximum voluntary strength was performed during 8 weeks 3-4 times a week. The frequency of the moves made 60 times per minute. In the course of morphometrical study greater attention was paid on mitochondrial parameters. Mitochondrial volume density did not change, while their number as well as the volume density of lipid inclusions tend to increase. Mitochondrial number, area and volume density of inclusions in the central zone of m. triceps surae were compared (before training: number per 100 microns2--2+3; area--0,13 +/- 0,010 microns2, volume density--2.7 +/- 0.3%, after training: number--48 +/- 4, area--0,110 +/- 0,01 microns2, volume density--2,7 +/- 0,3%) with the data available in literature on another muscles of elite sportsmen. It was concluded that high mitochondrial volume density in muscles of endurance trained sportsmen may result either from mitochondrial hypertrophy or increase of their number or from either of these factors, which is likely to be the concrete reflection of specificity of the sport efficiency.

Adult↗
PubMedDate not supplied

[The adaptation of human skeletal muscle fibers during aerobic training].

Effect of training on dimensions of muscle fibres of fast twitch and slow-twitch types were studied in three groups of subjects: local training of m. triceps surae (volunteers) in laboratory conditions, training of amateur joggers and of elite racers--skiers. Significant negative correlations between initial level and training-induced changes of muscle fibre cross sectional areas were demonstrated. The correlations found indicate that muscle fibre dimensions of people using similar endurance training programme tend to some certain level which is likely to be the optimal for this type of training. Dimensions of muscle fibre may significantly change as the result of traiining, probably, only in the case, when their initial values differ from the optimal one.

Adaptation, Physiological↗