Effect of membrane cholesterol on action of phospholipase A2 in Mycoplasma mycoides var. Capri. Evidence for lysophospholipase activity.

Cells of Mycoplasma mycoides var. Capri grown in a medium containing 10 micrograms/ml cholesterol (native organisms) or in cholesterol-free medium (adapted organisms) were treated with phospholipase A2. Hydrolysis of polar lipids (phosphatidylglycerol and diphosphatidylglycerol) only occurred in the adapted cells. Cholesterol replenishment of the membranes of these adapted cells in vitro which involves an increase from 7 micrograms to 66 micrograms cholesterol/mg membrane protein, completely abolished hydrolysis of polar lipid pools by phospholipase A2. This suggests that cholesterol incorporated either during growth or under conditions in vitro has an identical disposition and function in the membrane. This observation further indicates that cholesterol incorporation in M. mycoides var. Capri can be explained in terms of a simple physical adsorption process. Polar-lipid breakdown products resulting from phospholipase A2 action on intact cells, isolated membranes and lipids extracted from adapted organisms were analyzed. In experiments with intact cells [14C]oleic lysoderivatives but not [3H]palmitic lysoderivatives are accumulated within the membranes. In membrane preparations, again only [14C]oleic lysoderivatives are accumulated but transiently. Finally, both [14C]oleic and [3H]palmitic lysoderivatives were produced in phosphatidylglycerol-diphosphatidylglycerol liposomal preparations. From these results it can be concluded that: (a) 80% of the phosphatidylglycerol and diphosphatidylglycerol have an unusual positional distribution of their fatty acid (unsaturated oleic acid in position 1) and (b) membranes of M. mycoides var. Capri contain an active lysophospholipase which more efficiently hydrolyzes palmitic-acid-containing lysoderivatives.