Mycoplasma laidlawii

In this laboratory we have examined the ORD of various membrane systems including heavy beef heart submitochondrial vesicles, rat liver submitochondrial vesicles, erythrocyte ghosts, and the membranes of Micrococcus lysodeikticus, Halobacterium halobium, Halobacterium cuti-rubrum, and Mycoplasma laidlawii. The optical behavior of all these materials is strikingly similar the Cotton effects are similar to those produced by an a-helix but are red shifted to abnormally high wavelengths (71). Cotton effects arising from amide transitions in other... 

The method of biosynthetic incorporation of spin label, rather than mechanical addition to isolated material, is a convenient way of ensuring that the results obtained are biologically meaningful and has also been used with such systems as the mould Neurospora crassa [158], Mycoplasma laidlawii [159], human leucocytes, and mouse L cells [160]. The spectra from these two mammalian cells showed distinct similarities for a variety of spin labels, but different spectra were obtained when the labels were incorporated in human erythrocytes. Fractionation of the cell components showed the stearic acid (C, n = 3) spin label in all the major fractions, but by far the largest concentration was in the nuclear membrane. The ESR spectrum underwent a time and temperature dependent decay and spin labels on the surface membrane were reactivated with K3Fe(CN)6. 

The MW of the NADP-specific GDH of Neurospora has been shown to be 280,000-296,000 by sedimentation equilibrium analysis (Wootten, 1973) while the amino acid sequence (Wootten et al., 1974) shows that the polypeptides possess 50 residues less than those of the bovine liver enzyme, and that each subunit has a MW of 48,438 showing that this enzyme also is hexameric. The NADP-specific enzymes of Baker s yeast, E. coli, and the enzyme of dual coenzyme specificity from Mycoplasma laidlawii have been shown to have molecular weights similar to the Neurospora NADP enzyme, while SDS electrophoresis has shown their subunits are also of a similar size (Smith et al., 1975). 

From Table I it can be seen that the pH optima for deamination and amination reactions for enzymes from a number of sources are broadly similar. The amination reaction for most GDH s is optimal near pH 7.6-S.2, whereas for the deamination reaction the pH optimum is near S.5-9.5. Notable exceptions to this general pattern are the yeast NADP enzyme, and enzymes from Mycoplasma laidlawii and pea root. It has been pointed out that variations in pH optima can be due to the use of substrate concentrations in the assay system which are not sufiiciently high to reflect V ,ax values (Smith et ai, 1975). Apart from these exceptions, the differences in the pH optima for aminating and deaminating reactions are around 1.0-1.5 pH units, and this has important implications for the proposed reaction mechanism (Section II,D,4). 

These polyenes injure fungi by binding to the ergosterol and sitosterol of the plasma membranes (Hamilton-Miller, 1973). Mycoplasma laidlawii was unaffected by filipin when grown in the absence of the sterol, but lysed when grown in its presence (Weber and Kinsky, 1965). When polyene antibiotics were injected under mixed lipids, present as a monolayer in a surface-trough, it was found that the polyene interpenetrated the film and increased its area. Reorientation of the sterol component, caused by interaction with the polyene, seemed to make the film leaky (Demel, Van Deenen and Kinsky, 1965). Mitochondrial and nuclear membranes are not affected by the polyenes, nor is the cell wall (Kinsky, 1962). 

Gourlay RN. Isolation of a new virus infecting strain of Mycoplasma laidlawii. Nature. 1970 225 1165. 

D. Engelman, X-Ray Diffraction Studies of Phase Transitions in the Membrane of Mycoplasma Laidlawii, /. Mol Biol 41, 115-117 (1970). 

Structural independence of membrane lipid chains and protein shown by PMR, ORD, and CD in erythrocyte (Glaser et al., 1970), and by calorimetry in Mycoplasma laidlawii (Reinert and Steim, 1970 Melchior et al., 1971) is inherent to the model in Fig. 12 which includes the central lipid bilayer revealed by X-ray in many membranes (Section II,B). Attack by phospholipase C is made possible by thermal... 

The effects of variations in the fatty acid composition of membranes on the function of membrane-bound enzymes have been investigated in limited instances, under physiological conditions. For example, with mutant Saccharomyces cerevisiae species which cannot synthesize unsaturated fatty acids, depletion of unsaturated fatty acids inhibits mitochondrial oxidative phosphorylation (Haslam, 1971). This does not result from decreased synthesis or activity of any mitochondrial enzyme but represents an uncoupling between substrate and NAD/NADFl metabolism and the ability to synthesize ATP. It is also of interest that the morphology of Mycoplasma laidlawii is susceptible to variation as a function of the fatty acid composition of its membranes (Steim et al., 1969). 

Melchior, D. L., Morowitz, H. J., Sturtevant, J. M., and Tsong, T. Y., 1970, Characterization of the plasma membrane of Mycoplasma laidlawii. VII. Phase transitions of membrane lipids, Biochim. Biophys. Acta 219 114. 

Razin, S., Morowitz, H. J., and Terry, T. H., 1965, Membrane subunits of Mycoplasma laidlawii and their assembly to membrane-like structures, Proc. Natl. Acad. Sci. USA 54 219. 

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