Effect of Phospholipase C Hydrolysis of Membrane Phospholipids on Membranous Enzymes

The response of several Escherichia coli membranous enzymes to hydrolysis of up to 95% of membrane phospholipid has been investigated. Purified phospholipase C of Bacillus cereus was utilized in these studies. The rate and extent of digestion of E. coli phospholipids was independent of whether the lipid was associated with membrane protein or extracted from membranes and sonically dispersed. Phosphatidylethanolamine and phosphatidylglycerol were completely hydrolyzed, while cardiolipin was partially resistant to hydrolysis by phospholipase C. Acyl-CoA:glycerol 3-phosphate acyltransferase and NADH oxidase were inactivated at a rate very similar to the rate of hydrolysis of total lipids. Acyl-CoA:1-acylglycerol 3-phosphate acyltransferase was inactivated to an extent of 50% during hydrolysis of 50% of membrane phospholipid. The remaining activity was stable to continued hydrolysis of phospholipid. Glycerol 3-phosphate dehydrogenase and succinic dehydrogenase remained completely active after hydrolysis of 95% of membrane phospholipids. These results show the heterogeneity of membranous enzymes with respect to their dependence upon the presence of intact membrane phospholipids. The lack of effect of membranous lipid-protein interactions on the accessibility of phospholipids to phospholipase C hydrolysis was shown in general by the similarity in the rates of hydrolysis by phospholipase C of membranous and isolated phospholipids. More specifically, the similarity in the rate of hydrolysis of phospholipids and the rates of inactivation of certain membranous enzymes suggests that these enzymes are dependent on phospholipids whose susceptibility to phospholipase C hydrolysis is similar to the bulk of membrane phospholipids.