THE CELL-MEMBRANE OF MYCOPLASMA PENETRANS - LIPID-COMPOSITION AND PHOSPHOLIPASE A(1) ACTIVITY

Analysis of Mycoplasma penetrans membrane lipids revealed that, in add ition to large amounts of unesterified cholesterol, M. penetrans incor porated exogenous phospholipids, preferentially sphingomyelin, from th e growth medium. The major phospholipids synthesized de novo by M. pen etrans were phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG) . In vivo labeling of PG and DPG by growing the cells with radioactive palmitate or oleate, followed by snake venom phospholipase A(2) treat ment, enabled us to assess the positional distribution of fatty acids in these lipids. Saturated fatty acids were found preferentially in po sition 2 of the glycerol backbone, and not in position 1 as found else where in nature, while unsaturated fatty acids prefer position 1. M. p enetrans membranes contain phospholipase activity of the A(1) type, re moving a fatty acid from the sn-1 ester bond of phospholipids. The act ivity was neither stimulated by Ca2+ nor inhibited by EGTA and had a b road pH spectrum. The substrate specificity of the enzyme was investig ated with various natural lipids and with a fluorescent analog of the phosphatidylcholine. The enzyme was equally active toward phosphatidyl choline and phosphatidylglycerol, but did not hydrolyze diphosphatidyl glycerol. The enzyme did not act on triacylglycerol, diacylglycerol or cholesteryl ester, but low activity was detected toward monoacylglyce rol. The enzyme was heat-sensitive and detergent-sensitive, and was al most completely inhibited by p-bromophenacylbromide (50 mu M), but was not affected by SH reagents. This study is the first one reporting ph ospholipase A(1) activity in Mollicutes. A possible role of this enzym e in forming lipid mediators upon the interaction of M. penetrans cell s with eukaryotic cells is suggested.