Observations on membranes of Mycoplasma laidlawii strain B

Lipid and lipopolysaccharide composition of Acholeplasma oculi

The total lipid content of Acholeplasma oculi comprises 13.3% of the dry weight of the organism and is about equally distributed between the neutral lipids plus glycolipids and the phospholipids. The phospholipids were identified as phosphatidyl glycerol and diphosphatidyl glycerol. The glycolipid fraction contained O-alpha-D-glucopyranosyl-(1 leads to 1)-2,3-diacyl glycerol and O-alpha-D-glucopyranosyl-(1 leads to 2)-O-alpha-D-glucopyranosyl-(1 leads to 1)-2,3-diacyl glycerol. The neutral lipid contained pigmented carotenoids. Hot aqueous phenol extraction of lipid-extracted whole cells yielded a polymeric carbohydrate comprising 2.3% of the dry weight of the organism. The A. oculi lipopolysaccharide was found to contain only neutral sugars and no amino sugar, in contrast to other acholeplasmas. The neutral sugars consisted of fucose, galactose, and glucose in a ratio of 2:19:3.

Proteins selectively released from water-extracted human erythrocyte membranes upon citraconylation or maleylation. Electrophoretic analysis and chromatographic fractionation

1. Citraconylation or maleylation (carboxylation) of water-extracted human erythrocyte membranes (membrane residue) solubilized up to 20% (w/w) of the membrane residue protein, but less than 2% of the phospholipids. Amino acid analysis and polyacrylamide gel electrophoresis in the presence of dodecylsulfate showed that the solubilization was selective. 2. Polyacrylamide gel electrophoresis in the absence of detergent separated the solubilized acylated proteins into four well-separated major zones and two or three minor zones. Two of the major zones contained proteins of high molecular weight (spectrin components) and the other two contained components of intermediate molecular weight. 3. The solubilized components of intermediate molecular weight could be partially purified by hydroxyapatite chromatography. 4. Upon incubation at pH 5 and 36 degrees C of the unfractionated proteins solubilized by citraconylation some components became specifically degraded or dissociated into subunits.

Immunological analysis of glycolipids and lipopolysaccharides derived from various mycoplasmas

The lipids and lipopolysaccharides of five mycoplasmas were examined for complement-fixing activity to antimembrane rabbit sera. Total glycolipid fractions and the aqueous phenol fractions (lipopolysaccharides) from the membranes of Acholeplasma laidlawii, A. modicum, A. axanthum, and Mycoplasma neurolyticum exhibited significant antigenic activity. The glycolipids and phosphoglycolipids from Thermoplasma acidophilum were either anticomplementary or did not react due to their extreme hydrophobic nature. High activity was found using the lipopolysaccharide of T. acidophilum. The pure glycolipids and phosphoglycolipids of the Acholeplasma and Mycoplasma species also exhibited significant complement-fixing activity. Acylation of the sugar residues of these lipids reduced or negated complement-fixing activity. Double cross-reactions between the glycolipids of A. laidlawii and A. modicum appeared to be due to mono- and diglucosyl diglycerides of identical structure. Specificity of glycolipid structure was noted by the absence of cross-reactions between A. laidlawii and M. neurolyticum, the glycolipids of which differ only in the nature of the glucose linkages. The existence of lipopolysaccharides in the membranes of mycoplasmas and their complement-fixing activity in the presence of antimembrane sera suggest their possible importance as specific antigenic determinants.

Characterization of the membranes of Thermoplasma acidophilum

Thermoplasma acidophilum grows optimally under aeration at 59 C and pH 2. Both intact cells and membranes disaggregate below pH 1 and above pH 5, producing no sedimentable particles. Increase in ionic strength at pH 5 or below results in cellular lysis and membrane disaggregation. Membranous components produced by lysis at alkaline pH reaggregate upon reduction of both pH and ionic strength. Osmotic environment plays little role in cellular stability. Membranes prepared by sonic lysis at pH 5 exhibit vesicular structures and are composed of multiple proteins. Although the amino acid composition of the membrane proteins is similar to other mycoplasmal membranes, the number of free amino and carboxyl groups is less than half of those in Acholeplasma. Reduction of the number of free carboxyl groups results in membrane stabilization over a wide range of pH. Increase in the number of free amino groups reverses the stability of membranes relative to pH. Acidophily in Thermoplasma can be related to a significant reduction in repulsing negative charges on the membrane proteins.

Divalent cations in native and reaggregated mycoplasma membranes

The Mg(2+) content of membranes of several Mycoplasma and Acholeplasma species varied between 0.88 and 1.98 mug of Mg(2+) per mg of protein, depending on the species and on growth conditions. Ca(2+) could be detected only when it was added to the growth medium. The Mg(2+) content of isolated A. laidlawii membranes could be increased almost threefold by dialysis against 20 mm Mg(2+), whereas aggregated A. laidlawii membranes contained about six to eight times more Mg(2+) per mg of protein than the native membranes. This was taken to indicate that the molecular organization of the lipid and protein in the reaggregated membranes differs from that of the native membranes. Between 60 and 83% of the Mg(2+) in native and reaggregated A. laidlawii membranes was associated with the lipid fraction extracted with chloroform-methanol. The removal of over 80% of membrane protein by Pronase digestion did not release any significant amount of Mg(2+). Hence, most of the divalent cation appears to be bound to membrane lipids, most probably to phospholipids. Ethylenediaminetetraacetic acid released the bulk of Mg(2+) bound to the native and reaggregated A. laidlawii membranes, except for about 0.5 mug of Mg(2+) per mg of protein which was too tightly bound. Hence, a small but fairly constant amount of Mg(2+) is unavailable for chelation.

Kinetics of sodium dodecyl sulfate solubilization of Mycoplasma laidlawii plasma membranes

The kinetics of sodium dodecyl sulfate solubilization of aqueous suspensions of Mycoplasma laidlawii membranes have been investigated by light scattering in a stopped-flow apparatus. There was evidence of direct interaction between the membranes and sodium dodecyl sulfate micelles above the critical micelle concentration, although of lower order kinetically than with monomeric dodecyl sulfate anions below the critical micelle concentration. The activation energy remained the same in either case, about 10 kcal/mol. Static light-scattering studies at higher resolution showed that the solubilized membranes are in the form of small aggregates.