Biomedical subjects

A S Tikhonenko

Publications and source records attributed to A S Tikhonenko.

66 records · Page 4Linked to original sources

PubMedDate not supplied

[Structure of the interphase chromatin in the ciliata Bursaria truncatella macronucleus. II. Loop organization of inactive chromatin clumps].

Electron microscopic study of chromatin organization in isolated macronuclei of a ciliate Bursaria truncatella showed macronuclear chromatin to be organized in compact clumps 120--180 nm in diameter linked with each other by one or several chromatin fibres. Macronucleus being dispersed in a solution of low ionic strength, radial loops basically of nucleosomal structure start appearing around chromatin clumps. Long-time dispersing of macronuclear chromatin brings complete decompactization of chromatin clumps into a set of nucleosome fibres. The way the fibres of interphase chromatin are packed in a chromatin clump is discussed.

Cell Nucleus↗

PubMedDate not supplied

[Structure of the macronucleus chromatin of the ciliate Bursaria truncatella. III. Chromatin organization in resting cysts and during excysting].

Structural organization of macronuclear chromatin of a ciliate Bursaria truncatella was studied electronmicroscopically by means of Miller's technique and negative staining of resting cysts and at excysting. In resting cysts practically all the macronuclear chromatin was shown to be organized into compact chromatin clumps 100-300 nm in size. At excysting a natural decompactization of the chromatin clumps occurred and radial loop-shaped chromatin fibres appeared around the clumps. Sometimes transcription units with a relatively small contour length of transcribed region and with high RNA-polymerase density were observed on the loops. The responsibility of such genes for the synthesis of proteins taking part in regulation of excystment and/or subsequent cell growth and differentiation is discussed.

Animals↗

PubMedDate not supplied

[Fine structure of the outer sheath of the aerial mycelium in Actinomyces levoris].

The outer sheath of the aerial mycelium of Actinomyces levoris 64 bears groove-like and granular submicroscopic structures. They are very susceptible to a short-term treatment of the aerial mycelium with aqueous acetone which causes their disintegration. Under specified conditions, submicroscopic structures, viz. granules and threads, assemble from the acetone extract of the aerial mycelium of Actinomyces levoris. These structures possess the anti-yeast activity. The granular structures reorganized from the acetone extract of the aerial mycelium of Actinomyces levoris somewhat resemble in morphology the structures seen in the outer sheath of the aerial mycelium of this actinomycete. The results obtained are discussed within the framework of the hypothesis on a possible participation of polyene antibiotics in the formation of the outer sheath of the aerial mycelium of actinomycetes which produce these antibiotics.

Acetone↗

PubMedDate not supplied

[Study of the effect of different concentrations of a detergent on the chromatin structure of Physarum polycephalum during the mitotic cycle].

The influence of different concentrations of detergent Joy on the chromatin structure of Physarum polycephalum in the process of mitotic cycle was studied electronmicroscopically. The investigations showed that at Joy concentrations less than 0,01% a small part of nuclei disrupt and, as a rule, chromatin is insufficiently dispersed; at concentrations more than 0,1% the detergent may influence the chromatin structure of Physarum polycephalum. Based on the data obtained we consider that the optimal detergent concentrations that practically do not influence the chromatin structure and lead to disruption of the majority of nuclei and to the proper dispersion of chromatin is 0,1-0,01%.

Cell Division↗

PubMedDate not supplied

[Virulent and temperate phages of Bacillus licheniformis, the producer of bacitracin antibiotic].

Virulent and temperate bacterial phages were isolated from the cultural broth of Bacillus licheniformis obtained under the industrial conditions when synthesis of the antibiotic bacitracin was interfered with. The following properties of the phages were studied: the fine structure, the morphology of negative colonies, the spectrum of lytic action, the rate of adsorption, the individual growth cycle, as well as the lysogenic state of certain strains of Bac. licheniformis. Some phages were serologically related and morphologically identical whereas others differed sharply in their morphology and antigenic properties.

Bacillus↗

PubMedDate not supplied

[Electron microscopic study of the action of submicroscopic levorin structures on Candida guillermondii].

In the course of preparation of aqueous solutions of the polyene antibiotic levorin, the latter is recovered in the solid phase forming granular submicroscopic structures. If the cells of Candida guilliermondii are treated with submicroscopic granular structures (SMGS) of levorin, the structures are adsorbed on the surface of the yeast cell walls. Some visible changes occur in the ultrastructure of the yeast cells incubated with SMGS of levorin for 5 min: the inner layer of the cell wall becomes loose, the periplasmic space appears, the cytoplasmic membrane becomes thicker, the mitochondria swell, and fragmentation of the mitochondrial cristae takes place. Dense round alien bodies 20--40 mn in size can be discerned in the periplasmic space of such cells. If the yeast cells are treated with the levorin structures for a longer period of time (15--60 min), the cell ultrastructure is entirely disorganized.

Adsorption↗

PubMedDate not supplied

[Electron microscopic study of transcription of loach oocyte ribosomal genes].

Transcription of ribosomal genes of a loach Misgurnus fossilis L. was studied by electron microscopy. Relative transcriptional activity in nucleoli at different vitellogenic stages was determined by direct calculation of the number of operating ribosomal genes in the nucleoli. Morphologic studies showed that the transcribing regions of mean length 2.3 +/- 0.2 mkm are separated by spacers of variable lengths. Both short (1.2--1.4 micrometer) and long (2.4--2.6 micrometer) spacers were visualised. The lateral RNP fibrils have granular structure, each granule containing 300--350 RNA bases. It was found that chromatin has nucleosomal structure in spacer regions and is of non-beaded, smooth structure in transcribing regions. The data obtained allow to suggest that in transcribing regions chromatin undergoes structural transition before the transcription process.

Animals↗

PubMedDate not supplied

[Structure of polyriboguanylic acid in solution].

The electron microscopic data and the CD spectra of poly(G) have shown that the transition of a freeze-dried preparation of poly(G) from a "metastable" to a "stable" form is the transition of the four-stranded poly(G) from the globular form to the linear one. The observed phenomenon of the formation of long four-stranded poly(G) fibers (4--5 nm in diameter and 200-2000 nm in length) is suggested to be a result of a joint of the initial poly(G) molecules (50--80 nm in length) due to noncovalent binding ("sticking") of their free one-, double- or three-stranded ends. This phenomenon has permitted us not only to compare the thickness of low molecular weight poly (G) preparations under different conditions but to observe directly the existence of a large number of double-stranded (2--3 nm in diameter) regions ("defects") in four -stranded poly(G) fibers. The data obtained have shown that under certain conditions (high temperature, low pH, etc.) the four-stranded poly(G) fibers break down with the formation of two-stranded poly(G) fibers whose hydrogen bond systems depend on the conditions of their formation.

Chemical Phenomena↗

PubMedDate not supplied

[Study of the quaternary structure of glutamate carboxylase from Escherichia coli].

It was shown by electron microscopy, that the native molecule of glutamate decarboxylase is a hexamer with dihedral symmetry; the subunits are situated at the apices of an octahedron. Apoenzyme at pH 6.0 is dissociated form. It were found s20.w - 12.8 +/- 0.54S and 5.51 +/- 0.43S for the native hexamer and a dissociated form, respectively. By column gel-filtration the molecular mass of the dissociated form was estimated as 105-106 kDa, this value corresponds to a dimer. There were 10 buried SH-groups per subunit in the hexamer, after dimer formation 8 of them became accessible. The reversible hexamer-dimer dissociation depends on pH and PLP. The pH dependences of the enzyme dissociation and activity are very similar. In the result of adding of 6 PLP equivalents to the dimers the reactivation and hexamer assembly were reached, the SH-groups burying preceded both these reactions. Effect of pH and PLP on the quaternary structure is known for some other PLP-enzymes. It may be the additional proof for the idea of a common ancestor for PLP-enzymes.

Chromatography, Gel↗

PubMedDate not supplied

[Isolation of bacteriophages of methane oxidizing bacteria and study of their properties].

Five strains of bacteriophages were isolated for the first time in the USSR from the water of ponds, the paste of methane oxidizing bacteria and the cultural broth of the experimental plant. The strains are specific of the following species: Methylostinus sporium, Methylosinus trichosporium, and Flavobacterium gasotypicum. Bacteriophages lysing Methylocystis impression. Methylomonas agile and Methylococcus capsulatus were not isolated so far. The fine structure of the phages, the shape of negative colonies, the spectrum of lytic activity, and serological properties were studied. The phages can be subdivided into two groups according to the morphology of virions, the shape of negative colonies and serological properties, or into three groups according to the spectrum of lytic activity.

Antigens, Viral↗

PubMedDate not supplied

[Electron-microscopic study of the morphology of scaffold-like structures in chromosomes, formed by formamide].

Isolated human metaphase chromosomes treated with formamide and prepared for electron microscopy by protein monolayer technique have an appearance of loop-shaped chromatin fibers coming off the central scaffold-like structures, such chromosomes having approximately the same histone content as those before treatment. The morphology of scaffold-like structures at different formamide concentrations is described. It is shown that during formamide treatment the protein-protein and/or protein-DNA interactions are weakened because of disruption of hydrogen bonds. However, the intermolecular interactions in the chromosomes allow them to preserve their shape and size. The changes in the structure of formamide-treated chromosomes become readily visible after spreading on the hypophase surface. It is shown that after removal of formamide from the incubation solution by dialysis, chromosomes condense drastically. The data obtained are in good agreement with the loop model of chromosome organization. However they evidence also that the scaffold in the form of a rigid characteristic chromosome structure arises as a result of redistribution and/or aggregation of chromosomal proteins during chromosome preparation.

Cell Line↗

PubMedDate not supplied

[Ultrastructure of bacteriophages specific for Bacillus thuringiensis var. galleriae].

Fine structure of the phage specific for Bacillus thuringiensis var. galleriae was studied. The head of the phage is of the elongated hexagonal shape, 600 X 360 A. The tail is 400 X 40 A large and has a thickening in the basal part (70 X 120 A). A so-called "collar" structure is found at the site where the head joins the tail. This a disc-shaped plate with a diameter of 120 A and a hole in the centre; 12 fillaments are attached to it radially and terminated with tines. It is possible that the structure is necessary for adsorption of the phage on the cell.

Bacillus thuringiensis↗