Studies on Enzymes Involved in the Catabolism of Phospholipids in Escherichia coli

The hydrolysis of specifically labeled phosphatidylethanolamine and the 1 and 2 isomers of lysophosphatidylethanolamine catalyzed by enzymes in three subcellular fractions of Escherichia coli (wall, inner membrane and cytosol) has been studied. Two hydrolytic activities, phospholipases A1 and A2, are localized in the wall. Both enzymatic activities manifest similar properties and requirements for optimal activity, but it remains to be established whether both reside in the same enzyme. A hydrolytic activity toward the 1-acyl isomer of lysophosphatidylethanolamine is also present in the wall but it is unlikely that this activity can be ascribed to another catabolic enzyme. Rather, it appears that the phospholipase A1 also acts on the 1-acyl isomer of lysophosphatidylethanolamine. A lysophospholipase A2 that catalyzes the hydrolysis of the 2-acyl isomer of lysophosphatidylethanolamine to fatty acid and glycerophosphorylethanolamine was detected in the inner membrane of E. coli. A lysophospholipase A1 was also detected in the membrane, as well as in the cytosol fraction. The presence in the supernatant fraction of a phospholipase that was active on phosphatidylglycerol, but inactive on phosphatidylethanolamine, was confirmed. Also present in the supernate is a phosphodiesterase that catalyzes the hydrolysis of glycerophosphorylethanolamine to sn-glycerol 3-phosphate and ethanolamine. Thus the cell-free extract of E. coli contains all of the enzymes necessary for the complete degradation of phosphatidylethanolamine to fatty acids, sn-glycerol 3-phosphate, and ethanolamine.