Membrane Lipid Metabolism in Acholeplasma laidlawii A EF 22

Abstract

1. Membrane lipid metabolism in Acholeplasma laidlawii A EF 22 has been studied under different conditions by applying three different techniques for changing membrane viscosity : fatty acid and cholesterol supplementation and temperature changes.2. The molar relationship between the two dominating membrane lipids, monoglucosyldiglyceride and diglucosyldiglyceride, is to a large extent determined by membrane viscosity properties. This is shown by the varying metabolic responses occurring during incorporation of different fatty acids with and without cholesterol and by temperature shift-down experiments. Higher viscosity in membranes stimulates synthesis of monoglucosyldiglyceride at the expense of diglucosyldiglyceride. Synthesis of phospho and phosphoglucolipids is affected as well.3. Temperature shift-down from 37 'C to 17 "C results in an immediate synthesis of monoglucosyldiglyceride accompanied by an increased incorporation of unsaturated fatty acids into this lipid. Synthesis of the other membrane lipid species (containing more unsaturated fatty acids) lags behind temporarily.4. Incorporation from an equimolar mixture of palmitic and oleic acids together with cholesterol yields greater amounts of oleic acid in membrane lipids than incorporation in the absence of cholesterol, indicating that incorporation is viscosity dependent.5. Studies of precursor relationships reveal that all main lipids have an active turnover which differs depending on membrane composition and conditions. Furthermore, this turnover proceeds with different intra-lipid pools.6. Isolated membranes contain no detectable lipolytic enzymes capable of hydrolyzing membrane phospho or glycolipids. It is suggested that lipid turnover is partly mediated by enzymatic interlipid conversions, thus not allowing intermediates to accumulate.

Metabolic changes of membrane lipid composition in Acholeplasma laidlawii by hydrocarbons, alcohols, and detergents: arguments for effects on lipid packing

“…Since MGDG is the only lipid that alone with water can form nonlamellar phase structures, it is a key component in determining the phase equilibria of the in vivo mixtures. The ratio MGDG/DGDG in the A. laidlawii membrane is extensively regulated upon alterations of the growth conditions (Wieslander & Rilfors, 1977;Christiansson & Wieslander, 1978, 1980; Christiansson et al, 1981;Rilfors, 1985;Clementz et al, 1986). The regulations can be explained by the phase equilibria in MGDG-water, MGDG-DGDG-water, and in vivo total polar lipid-water mixtures, and hence by the ideas of lipid molecular geometry (Wieslander et al, 1980(Wieslander et al, , 1981aRilfors, 1985;Lindblom et al, 1986).…”

“…The membrane lipid composition in Acholeplasma laidlawii is regulated in response to changes of several environmental conditions. The conditions chosen in previous investigations were mainly of the kind that the organism will meet in its biological surroundings, such as changes in the growth temperature and the presence of cholesterol and different fatty acids used in membrane lipid synthesis (Wieslander & Rilfors, 1977;Christiansson & Wieslander, 1978, 1980Rilfors, 1985). One important aim of this regulation is to maintain a stable lipid bilayer structure during various environmental conditions (Wieslander et al, 1980(Wieslander et al, , 1981aRilfors et al, 1984;Rilfors, 1985).…”

Reversed cubic phase with membrane glucolipids from Acholeplasma laidlawii. Proton, deuteron, and diffusion nuclear magnetic resonance measurements

“…To obtain lipids containing only cis-unsaturated acyl chains, the growth medium was supplemented with 150 µ oleic acid (Wies- lander & Rilfors, 1977; and the cells were harvested after growth for 36 h at 30 °C. This temperature has the effect of increasing the relatively low amounts of MGDG normally obtained with oleic acid supplementation (Christiansson & Wieslander, 1978). Lipids containing approximately equal amounts of an unsaturated and a saturated acyl chain were obtained by supplementing the medium with 75 µ oleic acid and 75 µ palmitic acid and growing the cells for 24 h at 37 °C (Wieslander & Rilfors, 1977;.…”

Studies on the phospholipid composition of pathogenic cell membranes of Mycoplasma hyopneumoniae

“…Little was known about the membrane phospholipids of M. hyopneumoniae. The results showed that PG and DPG were the major phospholipids in membrane of mycoplasma cells except A. iaidfawii where glycophospholipids were also found [13]. Only M. hominis (ATCC 15056) contained PG, phosphatidic acid (PA) and lysophosphatidylglycerol (LPG) [14].…”