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S Razin

Publications and source records attributed to S Razin.

At least 19 recordsLinked to original sources
PubMed1992

Peculiar properties of mycoplasmas: the smallest self-replicating prokaryotes.

Mycoplasmas are the smallest and simplest prokaryotes capable of self-replication, with information provided by a genome which may be as small as 600 kb, estimated to carry less than 500 genes. Keeping the number of structural elements, metabolic pathways and components of the protein synthesizing machinery to an essential minimum places mycoplasmas closest to the concept of 'minimum cells'. Mycoplasmas are, therefore, most adequate candidates for the complete deciphering of the machinery of a self-replicating organism, and studies towards this goal are already underway. Living as 'minimum cells' was made possible by adopting a parasitic mode of life, securing from the host the many nutrients which cannot be synthesized by the mycoplasmas themselves. When pathogenic, infections by mycoplasmas usually follow a chronic course, with host immune reactions playing an important role in symptom production. Recent studies on the possible association of mycoplasmas with rheumatoid arthritis and AIDS are reviewed.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Nucleotide sequence and codon usage of the elongation factor Tu(EF-Tu) gene from Mycoplasma pneumoniae.

The Mycoplasma pneumoniae tuf gene, encoding the elongation factor protein Tu, was cloned and sequenced. The nucleotide sequence of the mycoplasmal gene showed about 60% homology to the sequences of tuf genes of other prokaryotes, yeast mitochondria and Euglena gracilis chloroplasts, and about 75% similarity was found when comparing the deduced amino acid sequences of the various Tu proteins. The relatively low G + C content (40%) of the M. pneumoniae DNA was reflected in a low G + C content (44.6%) of the tuf gene, and in a preferential use of adenine and uracil at the third position of codons, yet codon usage analysis revealed the presence of almost all of the codons of the genetic code in the mycoplasmal gene. Southern blot hybridization of digested DNAs of 11 Mollicutes species with the entire M. pneumoniae tuf gene and with its 5' part suggested the presence of one copy only of this gene in the representative species of the Mollicutes. In this respect, the Mollicutes resemble Gram-positive bacteria and differ from the Gram-negative bacteria, which carry two copies of the tuf gene.

Amino Acid Sequence↗
PubMed1979

Is the vertical disposition of Mycoplasma membrane proteins affected by membrane fluidity?

The influence of the physical state of the membrane lipid matrix on the vertical disposition of membrane proteins was studied with Acholeplasma laidlawii. Changes in membrane fluidity were brought about by altering the fatty acid composition of membrane lipids, by changing the growth temperature, by aging of cultures and by inducing changes in the membrane lipid-to-protein ratio through treatment with chloramphenicol. The lactoperoxidase-mediated iodination technique was used to label membrane proteins exposed to the aqueous surroundings. The degree of exposure of the iodine-binding sites of membrane proteins on the external surface of intact cells was found to undergo significant changes on varying growth conditions, but the changes could not be consistently correlated with changes in membrane fluidity, nor were they discernible on iodination of isolated membranes.

Acetates↗
PubMed1979

Adherence of Mycoplasma gallisepticum to glass.

Attachment of washed Mycoplasma gallisepticum cells to glass was quantified with organisms in which membrane lipids were labelled with 3H. Siliconization of the test tubes decreased attachment, while centrifugation increased it. Attachment increased with temperature, decreased with increasing pH and ionic strength of the attachment mixture, but was unaffected by Ca2+, Mg2+ and EDTA. This suggests that ionic bonds, but not salt bridges, participate in the attachment process. Glycophorin, the major receptor responsible for M. gallisepticum attachment to erythrocytes, partially inhibited the attachment of the organisms to glass. However, bovine serum albumin also decreased attachment. Extensive pretreatment of the organisms with trypsin decreased their ability to attach to glass by about 35 to 40%. Trypsin and pronase failed to detach the organisms already bound to glass, suggesting that external mycoplasma cell components, other than membrane proteins, also participate in attachment of the organisms to glass.

Cell Count↗
PubMed1979

Outer membrane proteins of smooth and rough strains of Proteus mirabilis.

The outer membranes of the smooth Proteus mirabilis S1959 strain and its rough R13, R110, R51 and R45 mutants were isolated by sonication of the cells and sucrose density gradient centrifugation. The outer membrane of the rough strains had a lower density than that of their parent smooth strain, but the protein-to-phospholipid ratios were the same. The electrophoretic patterns of outer membrane polypeptides of the S and R strains in sodium dodecylsulfate/polyacrylamide gels were identical, with two major polypeptide bands, C1 and C2 (Mr 39,000 and 38,000) predominating. The C1 polypeptide band was a heat-modifiable polypeptide, which migrated as a band at Mr 33,000 when membranes were solubilized at 37 degrees C or 50 degrees C, and at Mr 39,000 when solubilization was at 100 degrees C. Susceptibility of outer membrane polypeptides to proteolytic digestion was found to be higher in isolated outer membrane preparations of the rough strains than in the smooth strain, suggesting that the availability of the polypeptide chains to proteolytic activity depends on the length of the polysaccharide chains of the outer membrane lipopolysaccharide.

Cell Membrane↗
PubMed1979

Adherence of Mycoplasma pneumoniae to glass surfaces.

Attachment of M. pneumoniae to glass was quantitated in an experimental system enabling the settling down of [3H]palmitic acid-labeled cells onto glass cover slips. Attachment of mycoplasmas suspended in buffer increased with temperature, decreased with higher ionic strength, and showed a maximum at about pH 5.5. The findings suggest a participation of ionic bonds in the attachment process. Trypsin did not detach glass-bound mycoplasmas, and treatment of the cells with glutaraldehyde did not reduce their attachment to glass, suggesting that membrane components other than proteins may be involved in the attachment. Low concentrations (up to 20 mg/ml) of bovine serum albumin buffer. However, during the next few hours, attachment increased far above the bovine serum albumin control. This marked increase was reduced by more than half in the presence of chloramphenicol. Increased attachment was also observed when glucose (0.1 to 2 mg/ml) was added to the bovine serum albumin-containing buffer. The findings suggest different mechanisms for the attachment in protein-free buffer and in growth medium or glucose-containing bovine serum albumin buffer, respectively. The latter apparently requires metabolic activity of the mycoplasmas.

Culture Media↗
PubMed1979

Binding of lectins to membranes of mycoplasmas from aging cultures.

The binding of iodinated concanavalin A (Con A) and Ricinus communis agglutinin (RCA) to intact cells and isolated membranes of Acholeplasma laidlawii, Mycoplasma hominis and Mycoplasma capricolum decreased with the progression of the culture from the mid- to the late-logarithmic phase of growth. The binding of the lectins to Acholeplasma laidlawii membranes had no significant effect on membrane fluidity, as assessed by electron-paramagnetic resonance spectroscopy of spin-labelled fatty acids, and had no effect on several membrane-associated enzymic activities. Temperature affected the binding of Con A and RCA in an opposite manner: the binding of Con A increased, whereas that of RCA decreased, on raising the temperature from 4 degrees C to 37 degrees C. No significant difference in lectin binding was found between oleate- and elaidate-enriched membranes at low temperatures where the former was in the liquid-crystalline state and the latter in the gel state, suggesting that membranes fluidity does not influence the binding of Con A and RCA to Acholeplasma laidlawii membranes.

Acholeplasma laidlawii↗
PubMed1978

Cholesterol uptake is dependent on membrane fluidity in mycoplasmas.

The transfer of elaidate-enriched Acholeplasma laidlawii cells in culture from 37 degrees C to 4 degrees C virtually arrested exogenous cholesterol incorporation into the cell membrane. Cholesterol uptake continued, though at a slower rate, in oleate-enriched A. laidlawii cells undergoing similar temperature shift-down. It is concluded that the incorporation of exogenous cholesterol into the cell membrane of living mycoplasmas is rapid when the membrane lipid bilayer is in the liquid-crystalline state and very slow when the lipid bilayer is in the gel state.

Acholeplasma laidlawii↗
PubMed1978

Thermal regulation of the fatty acid composition of lipopolysaccharides and phospholipids of Proteus mirabilis.

The fatty acid composition of the lipid A moiety of the lipopolysaccharide and phospholipid fractions of Proteus mirabilis changed significantly on varying the growth temperature. A decrease in the growth temperature from 43 degrees C to 15 degrees C resulted in a decrease in the palmitic acid content of the lipopolysaccharide from 19.4% of total fatty acids at 43 degrees C to 1.4% at 15 degrees C, and by the appearance of an unsaturated fatty acid residue, hexadecenoic acid. Changes in the 3-hydroxy-myristic acid content of the lipid A were minimal. The decrease in the growth temperature also resulted in a decrease in the saturated fatty acid content of the phospholipid fraction, which was accompanied by an increase in their fluidity, as measured by the freedom of motion of spin-labeled fatty acids incorporated into dispersions made of the phospholipids. Nevertheless, the fluidity obtained with membrane phospholipids extracted from the cells grown at various temperatures were essentially the same when fluidity was determined at the growth temperature, supporting the hypothesis that variations in the fatty acid composition of membrane phospholipids serve to produce membranes having a constant fluidity at different temperatures of growth.

Chromatography, Gas↗
PubMed1978

Cerulenin-induced changes in the lipopolysaccharide content and phospholipid composition of Proteus mirabilis.

Inhibition of Proteus mirabilis growth by cerulenin, a specific inhibitor of fatty acid biosynthesis, was reversed by exogenously supplied fatty acid mixtures containing oleic acid and palmitic or pentadecanoic acids. The growth rate of the cells treated with cerulenin in the presence of the fatty acid mixtures was slower, however, than that of untreated cells, and their lipopolysaccharide content was decreased by 30-50%, resulting in an increased sensitivity of the organisms to rifamycin and vancomycin. Polyacrylamide gel electrophoresis of the lipopolysaccharide fraction from cerulenin-treated cells revealed that of the two P. mirabilis lipopolysaccharide types, the relative amount of the higher molecular weight lipopolysaccharide was reduced from 50% to 30% of the total lipopolysaccharide. Fatty acid analysis of the phospholipid and lipopolysaccharide fractions from cells grown with cerulenin, pentadecanoate, and oleate revealed that over 60% of the native even-numbered fatty acids of the phospholipid fraction was substituted by the odd-numbered fatty acid, while no incorporation of either the pentadecanoate or oleate could be demonstrated in the lipid A moiety of the lipopolysaccharide. The only change in the lipid A observed was an increase in the content of 3-hydroxymyristic acid accompanied by a decrease in the nonhydroxylated fatty acids, supporting the highly conserved nature of this molecule.

Antifungal Agents↗
PubMed1978

Adherence of Mycoplasma gallisepticum to human erythrocytes.

Pathogenic mycoplasmas adhere to and colonize the epithelial lining of the respiratory and genital tracts of infected animals. An experimental system suitable for the quantitative study of mycoplasma adherence has been developed by us. The system consists of human erythrocytes (RBC) and the avian pathogen Mycoplasma gallisepticum, in which membrane lipids were labeled. The amount of mycoplasma cells attached to the RBC, which was determined according to radioactivity measurements, decreased on increasing the pH or ionic strength of the attachment mixture. Attachment followed first-order kinetics and depended on temperature. The mycoplasma cell population remaining in the supernatant fluid after exposure to RBC showed a much poorer ability to attach to RBC during a second attachment test, indicating an unequal distribution of binding sites among cells within a given population. The gradual removal of sialic acid residues from the RBC by neuraminidase was accompanied by a decrease in mycoplasma attachment. Isolated glycophorin, the RBC membrane glycoprotein carrying almost all the sialic acid moieties of the RBC, inhibited M. gallisepticum attachment, whereas asialoglycophorin and sialic acid itself were very poor inhibitors of attachment. Only part of the (125)I-labeled glycophorin bound to mycoplasmas could be removed by neuraminidase or by exchange with unlabeled glycophorin. It is suggested that glycophorin, representing the isolated major RBC receptor for M. gallisepticum, binds to the mycoplasmas both specifically, through its sialic acid moieties, and nonspecifically, through its exposed hydrophobic polypeptide moiety.

Calcium↗
PubMed1978

The mycoplasmas.

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Bacterial Proteins↗
PubMed1977

Cholesterol-phosphatidylcholine dispersions as donors of cholesterol to Mycoplasma membranes.

Growing cells of sterol-requiring Mycoplasma hominis and sterol non-requiring Acholeplasma laidlawii were used to test the ability of cholesterol-dipalmitoyl phosphatidylcholine dispersions to serve as cholesterol donors to these organisms. Dispersions with high cholesterol to phosphatidylcholine ratios were more effective than dispersions with low cholesterol to phosphatidylcholine ratios in donating cholesterol to the membranes of both mycoplasmas and in promoting growth of the sterol-requiring species. M. hominis took up almost three times as much cholesterol as did A. laidlawii. In addition, significant quantities of the phosphatidylcholine component of the dispersions were found to be associated with M. hominis membranes as against none in the A. laidlawii membrane preparations. In all cases, the percentage of cholesterol taken up by M. hominis from the dispersions exceeded that of phosphatidylcholine by a factor of 3-5. These results were interpreted to suggest that all the cholesterol taken up by A. laidlawii is transferred from the dispersion to the membranes by a process which involves only a transient contact between the organisms and the lipid dispersions, whereas a certain amount of the cholesterol taken up by M. hominis may also be derived from lipid dispersions adhering to or fusing with the cell membranes.

Acholeplasma laidlawii↗