Comparison of the hydrolysis of phosphatidylethanolamine and phosphatidyl ( N-acyl) ethanolamine in Dictyostelium discoideum amoebae

Abstract

Listen

Translate article

In Dictyostelium discoideum, ( N-acyl)ethanolamine glycerophospholipids disappear as the amoebae aggregate, whereas the amount of ethanolamine glycerophospholipids remains relatively constant, suggesting that each type of ethanolamine-containing phospholipid might have a separate metabolic pathway. To study their metabolism, phosphatidylethanolamine and phosphatidyI( N-acyl)ethanolamine containing either [ 14C]ethanolamine or a 14C-labeled sn-2 fatty acyl group were incubated with D. discoideum homogenates, and the conversion of the substrates into radioactive products was monitored. At pH values 3.8 and 4.5, phosphatidyl( N-acyl)ethanolamine was hydrolyzed by a phospholipase A 1 to form the sn-2 acyl form of the lipid. Only minor hydrolysis occurred at pH values of 5.2 or higher. ( N-acyl)Ethanolamine was also released by a phospholipase D type activity at 0.1 the rate of the lysophospholipid formation. Phosphatidyl ( N-acyl)ethanolamine was not hydrolyzed to form phosphatidylethanolamine or water soluble components. At pH 7.2 and at the low pH range of 3.8–4.5, phosphatidylethanolamine was hydrolyzed to lysophosphatidylethanolamine, which was then further degraded to water-soluble components. At pH 7.2, a phospholipase A 2 initially hydrolyzed the phosphatidylethanolamine, whereas at the low pH range a phospholipase A 1 was the most active enzyme. Although both types of ethanolamine-containing phospholipid were hydrolyzed by a phospholipase A 1 at the low pH range, phosphatidylethanolamine hydrolysis was more sensitive to inhibition by Trition X-100, and phosphatidylethanolamine was hydrolyzed to water-soluble components, whereas phosphatidyl( N-acyl)ethanolamine was not. At pH 7.2, phosphatidylethanolamine was hydrolyzed, but phosphatidyl( N-acyl)ethanolamine was not hydrolyzed at all. These results indicate that there are separate routes of degradation for the two types of ethanolamine-containing phospholipid in D. discoideum.