—1,2‐Diacyl‐, 1‐alk‐1′‐eny1‐2‐acyl‐ and 1‐alky1‐2‐acyl‐sn‐glycero‐3‐phosphorylcholine specifically labelled with different fatty acids at the 2 position, were prepared enzymically using the acyltransferase system of rabbit sarcoplasmic reticulum. The substrates were submitted to hydrolysis by phospholipase A2 (phospholipid acyl‐hydrolase, EC 3.1.1.4) obtained from normal and brain tissue affected with subacute sclerosing panencephalitis. In the diseased tissue an increase of phospholipase A2 activity ranging from 46 to 54% could be observed in comparison to the control brain for all substrates investigated. Among the investigated substrates phospholipase A2 had the highest affinity for the 1,2‐diacylcompound, whereas alkenylacyl‐ and alkylacyl‐sn‐glycero‐3‐phosphorylcholine were cleaved at almost similar rates. The hydrolysis rate of choline‐plasmalogen and the corresponding diacyl compound by the enzyme was greatly influenced by the fatty acid moiety located at the 2 position of the substrates.

1,2-Diacyl-sn-glycero-3-phosphorylcholine, -ethanolamine and -serine, specifically labelled with different fatty acids at either the 1- or 2-position, were prepared enzymatically using the acyltransferase system of rat liver microsomes. The substrates were subjected to hydrolysis by phospholipase A2 obtained from brain tissue of a normal and a case of subacute sclerosing panencephalitis (SSPE). In the pathological tissue and increase of approx. 50% in phospholipase A2 activity could be observed in comparison to that from the control brain for all investigated substrates. Experiments with phosphatidylethanolamines, specifically labelled with different fatty acids in the 2-position, revealed that the phospholipase A2 activity of the SSPE brain tissue was enhanced by about 50% when compared to the control brain regardless of the fatty acid constituent at the 2-position of the substrates.

The effect of phospholipase A1 of human brain on 1,2-diacyl-sn-glycero-3-phosphorylcholine, -ethanolamine and -serine, specifically labelled with different fatty acids at either the 1 or 2 position, was determined in subacute sclerosing panencephalitis. An increase of approximately 40% in the specific activity of phospholipase A1 could be observed for all substrates investigated during the demyelinating disorder. On investigating the specific activity of the enzyme with various molecular species of phosphatidylcholine and -ethanolamine, labelled at the 1 position with different radioactive fatty acids, we found that the phospholipase A1 preferentially removed those fatty acids from the 1 position of phosphatidylcholines that have the fewest double bonds, while oleic and linoleic acid were released at almost similar rates from phosphatidylethanolamine.