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S Rottem

Publications and source records attributed to S Rottem.

At least 181 records · Page 10Linked to original sources
PubMed1971

Sterol requirements of T-strain mycoplasmas.

T-strain mycoplasmas are very sensitive to digitonin, amphotericin B, and progesterone. This sensitivity and the relatively high content of cholesterol found in the cells indicated a possible requirement of T-strain mycoplasmas for sterols. This suspected requirement was demonstrated directly in a lipid-poor medium and can be met by cholesterol, as well as by beta-sitosterol and to a lesser degree by 7-dehydrocholesterol, cholestanol, stigmasterol, and ergosterol but not by cholesterol laurate or cholestan-3-one. Coprostanol, epicoprostanol, and epicholestanol inhibited cell growth. This inhibition could be partially reversed by increasing the cholesterol concentration in the growth medium. Because of their sterol requirement and their unique requirement for urea, T-strain mycoplasmas might be classified as the third genus in the order Mycoplasmatales.

Ammonia↗
PubMed1969

Sugar transport in Mycoplasma gallisepticum.

Mycoplasma gallisepticum cells were found to contain two different sugar transport systems, one for d-glucose and alpha-methyl-d-glucoside (alpha-MG) and the other for d-mannose and d-fructose. Both systems were noninducible, stereospecific, dependent on temperature and pH, and sensitive to sulfhydryl-blocking reagents. The rate of sugar uptake depended on its external concentration, obeying Michaelis-Menten kinetics. The sugar accumulated in the cells against a concentration gradient, and an energy requirement for accumulation was demonstrated with alpha-MG. Both transport systems thus meet the criteria of active transport. The exit of alpha-MG from the cells, like its entry, depended on temperature and was accelerated by energy supplied by the oxidizable d-mannose. d-Glucose accelerated alpha-MG exit, apparently by an exchange reaction. A method for measuring the intercellular space and intracellular free-water volume of Mycoplasma was devised, and several of its applications are described.

Biological Transport, Active↗
PubMed1968

Amino acid transport in Mycoplasma.

The uptake of l-histidine by Mycoplasma fermentans and l-methionine by M. hominis was found to be dependent on temperature and pH and to follow saturation kinetics. Several metabolic inhibitors inhibited this uptake. The transport system for l-methionine was highly specific. The l-histidine transport system was less specific, and the uptake was competitively inhibited by l-arginine and l-lysine. l-Histidine accumulated in the intracellular pool of M. fermentans at a concentration about 200 times that found in the medium. Efflux of accumulated l-histidine was demonstrated at 37 C, but not at 0 C. The rate of efflux was greatly accelerated by addition of l-histidine to the medium. The findings indicate that the Mycoplasma cell membrane contains specific transport systems resembling the permease systems of other microorganisms.

Acetates↗
PubMed1967

Electrophoretic patterns of membrane proteins of Mycoplasma.

Cell membranes of Mycoplasma were isolated either by osmotic lysis or by ultrasonic disruption of the organisms. The membranes were dissolved in phenol-acetic acid-water (2:1:0.5, w/v/v), and membrane proteins were separated electrophoretically in polyacrylamide gels containing 5 m urea and 35% (v/v) acetic acid. The electrophoretic patterns of membrane proteins were highly specific for the different Mycoplasma strains examined. The use of this method to prove the identity or dissimilarity of Mycoplasma strains is suggested.

Bacterial Proteins↗
PubMed1967

Identification of Mycoplasma and other microorganisms by polyacrylamide-gel electrophoresis of cell proteins.

The proteins of Mycoplasma cells of various species produce highly reproducible and species-specific electrophoretic patterns in polyacrylamide gels containing 5 m urea and 35% acetic acid. These electrophoretic patterns can be used for the rapid identification and classification of Mycoplasma. Preliminary results indicate that this method may also be used for the identification and classification of other microorganisms.

Amides↗
PubMed1966

Adenosine triphosphatase activity of mycoplasma membranes.

Rottem, Shlomo (Hebrew University, Jerusalem, Israel), and Shmuel Razin. Adenosine triphosphatase activity of mycoplasma membranes. J. Bacteriol. 92:714-722. 1966.-Adenosine triphosphatase activity of Mycoplasma laidlawii, M. gallisepticum, and Mycoplasma sp. strain 14 was confined to the cell membrane. The enzymatic activity was dependent on magnesium, but was not activated by sodium and potassium. Ouabain did not inhibit the adenosine triphosphatase activity of the mycoplasmas, and did not interfere with the active accumulation of potassium by M. laidlawii cells. Sulfhydryl-blocking reagents and fluoride inhibited the enzymatic activity, whereas 2,4-dinitrophenol was without any effect. Membranes of M. laidlawii hydrolyzed other nucleotide triphosphates and adenosine diphosphate (ADP), but at a lower rate than adenosine triphosphate (ATP). Nucleoside-2'-(3')-phosphates, ribose-5-phosphate, glucose-6-phosphate, and pyrophosphate were not hydrolyzed by the membrane preparations. It seems that the enzyme(s) involved in ATP hydrolysis by M. laidlawii membranes is strongly bound to the membrane subunits, which would account for the failure to purify the enzyme by protein fractionation techniques. The adenosine triphosphatase activity of mycoplasma membranes resembles in its properties that of similar enzymes studied in bacteria. The mycoplasma enzyme(s) seems to differ from the adenosine triphosphatase associated with ion transport in mammalian cell membranes and from mitochondrial adenosine triphosphatase.

Adenosine Triphosphatases↗
PubMedDate not supplied

Physical state of membrane lipids of Mycoplasma capricolum.

The physical state of the lipids in Mycoplasma capricolum membranes was studied by differential scanning calorimetry. Cells grown in the presence of horse serum incorporated large amounts of cholesterol esters into their membranes. After incubation at a low temperature, the cholesterol ester-containing membranes showed an endotherm characteristic of a cholesterol ester transition from a crystalline state to an isotropic liquid that was identical in membranes both before and after thermal protein denaturation. This transition was not observed in membranes of cells grown in medium in which the horse serum was replaced by bovine albumin, fatty acids, and unesterified cholesterol unless cholesterol esters were added to the growth medium. In membrane preparations obtained from both horse serum-grown cells and from cells grown with bovine albumin plus cholesterol and fatty acids, the free cholesterol content was sufficient to eliminate the bilayer order/disorder transition observed in isolated membrane phospholipids. Our calorimetric studies indicate that the majority of cholesterol esters in M. capricolum membranes is not present in attached serum lipoprotein particles nor is it intimately associated with membrane protein but exists as relatively large droplets of cholesterol ester or as pockets in the membrane. The cholesterol esters in these pockets exist in a liquid-like state at growth temperature and appear to be relatively pure, although the presence of small amounts of other membrane components, especially glycerides, is likely. The existence of a low-temperature endotherm in membrane attributable to glycerides suggests there may be glyceride-rich regions in the membranes.

Animals↗
PubMedDate not supplied

Cholesterol and phospholipid uptake by mycoplasmas.

Mycoplasma offer several unique advantages for investigating the mechanism controlling transfer and uptake of exogenous cholesterol and phospholipids by biomembranes, as their plasma membrane interacts directly with exogenous lipid donors and their endogenous lipid synthesis is restricted. Growing cells of five species of Mycoplasma were found to take up significant quantities of phosphatidylcholine and sphingomyelin as well as free and esterified cholesterol. In contrast, growing cells of three species of Acholeplasma failed to take up any of the exogenous phospholipids and incorporated only low amounts of free cholesterol and no esterified cholesterol. It is hypothesized that Mycoplasma species have receptors for serum lipoproteins and phospholipid-cholesterol vesicles that facilitate the transfer of cholesterol and phospholipids to the growing cell membrane. Our finding that gentle trypsin treatment of growing Mycoplasma capricolum cells decreased their cholesterol uptake ability by about 50% but did not affect cholesterol uptake by growing Acholeplasma laidlawii cells appears to support the existence of protein receptors for lipoproteins on the surface of Mycoplasma but not on Acholeplasma species. Digestion of membrane phospholipids by phospholipase A2 decreased the cholesterol-binding capacity of isolated A. laidlawii and M. capricolum membranes, roughly in proportion to the amount of phospholipid digested. The total removal of phosphatidylglycerol and diphosphatidylglycerol from A. laidlawii membranes by phospholipase A2 only decreased but did not abolish cholesterol uptake, an indication that glycolipids also participate in cholesterol uptake.

Acholeplasma↗
PubMedDate not supplied

Molecular organization and selective solubilization of lipids and proteins in the envelope of mycoplasmal virus L2.

The composition and molecular organization of mycoplasmal virus L2 (MVL2) were studied and compared with those of the cell membrane of the host, Acholeplasma laidlawii strain JA1. The virus contained 0.2-0.25 mumol of polar lipids per mg of viral protein. The lipid species of the MVL2 were the same as those of the host cells. Nevertheless, the proportions between the various polar lipids were different, with a much lower content of phosphatidylglycerol in the viral lipids. Despite these quantitative differences, the fatty acid composition of MVL2 was similar to that found in the host cells, a similarly allowing alteration of the fatty acid composition and study of its effect on viral absorption, penetration, and release. Pulse-chase experiments revealed that the lipids incorporated into the virus were synthesized before and after infection. Electron paramagnetic resonance spectrometry suggested that the viral lipid domain had the properties of a lipid bilayer. Nevertheless, the hydrocarbon chains in the MVL2 envelope were less mobile than those in membranes of the host cells, a difference apparently due to the different content, composition, and disposition of proteins in the MVL2 envelope. The electrophoretic pattern of MVL2 polypeptides was dominated by four major and five minor bands distinct from the polypeptides present in A. laidlawii membranes. None of the polypeptides gave a positive periodic acid-Schiff reaction, a result suggesting the absence of glycoproteins. Selective solubilization experiments excluded the possibility that one or more of the major polypeptides was associated with a capsid structure. Lactoperoxidase-mediated iodination of intact viral particles revealed that at least two of the major polypeptides were localized on the external surface of the viral envelope. The susceptibility of these polypeptides to brief proteolytic treatment and the finding that the infectivity of the virus was dramatically affected by such treatment suggested that these polypeptides were playing a role in recognition and/or attachment of the virus to the host cells.

Acholeplasma laidlawii↗
PubMedDate not supplied

Phase separation, ion permeability, and the isolation of membranes from osmotically stable mycoplasmas.

The osmotic stability of M. gallisepticum was found to be a consequence of the synthesis of disaturated phosphatidylcholine incorporated into the cell membrane. The disaturated lipid induces the formation of segregated lipid domains, thus providing the sites for increased permeation of ions. Such permeation reduces the internal pressure so as to minimize cell swelling and subsequent lysis in a hypotonic medium. Purified membranes of M. gallisepticum can be prepared from cells suspended in an iso-osmotic NaCl solution containing either dicyclohexylcarbodiimide (DCCD), which blocks ATPase activity, or a mild alkaline buffer. Both conditions seem to interfere with cell volume regulation. These procedures can be used also to isolate membranes of other osmotically stable mycoplasmas.

Adenosine Triphosphatases↗
PubMedDate not supplied

Transbilayer distribution of sterols in mycoplasma membranes: a review.

The polyene antibiotic, filipin, binds to 3 beta-hydroxysterols. The initial rate of filipin-sterol association, monitored in a stopped-flow spectrophotometer, was first order in each reacting partner. The ratio of rate constants in intact mycoplasma cells relative to isolated, unsealed membranes provides an estimate of sterol distribution in the membrane bilayer. Cholesterol is distributed symmetrically in the bilayer of M. gallisepticum cells from the early exponential phase. However, in the M. capricolum membrane two-thirds of the unesterified cholesterol is localized in the outer leaflet; alkyl-sterols are distributed predominantly in the external monolayer. Cholesterol is translocated rapidly in the bilayer of M. capricolum cells. Exogenous phospholipids incorporated into the membrane had no effect on the cholesterol distribution in M. capricolum.

Cell Membrane↗