| Abstract: | Chylomicrons labeled with 3H]arachidonic and 14C]linoleic acid were incubated with bovine milk lipoprotein lipase or rat postheparin plasma, containing both lipoprotein lipase and hepatic lipase. During incubation with bovine lipoprotein lipase, 3H]arachidonic acid was released from chylomicron triacylglycerols at a slower rate than 14C]linoleic acid. Only small amounts of 14C]linoleic acid were found as 1,2(2,3)-diacylglycerols, whereas a transient accumulation as 14C]monoacylglycerols was observed. In contrast, significantly more 3H]arachidonic acid was found as 1,2(2,3)-diacylglycerols than as monoacylglycerols at all time intervals investigated. The initial pattern of triacylglycerol hydrolysis by postheparin plasma was similar to that of bovine lipoprotein lipase. However, in contrast to the results obtained with bovine lipoprotein lipase, little 3H]1,2(2,3)-diacylglycerol accumulated. The addition of antiserum to hepatic lipase increased the amount of 3H found in 1,2(2,3)-diacylglycerols and inhibited the formation of free 3H]arachidonic acid. The antiserum also caused a significant inhibition of the hydrolysis of 3H]-but not of 14C]triacylglycerol. With regard to chylomicron phospholipids, the rate of hydrolysis of 14C]linoleoyl phosphatidylcholine with milk lipoprotein lipase was twofold higher than that of the 3H]arachidonyl phosphatidylcholine. However, the hepatic lipase of postheparin plasma had similar activity towards the two phosphatidylcholine species. Postheparin plasma rapidly hydrolyzed chylomicron 3H-labeled and 14C-labeled phosphatidylethanolamine to the same degree, and lipoprotein lipase similarly hydrolyzed 3H-labeled and 14C-labeled phosphatidylethanolamine at approximately equal rates. Antiserum to hepatic lipase inhibited the postheparin plasma hydrolysis of phosphatidylethanolamine and 3H-labeled phosphatidylcholine by about 60%, but the 14C-labeled phosphatidylcholine by only 27%.(ABSTRACT TRUNCATED AT 250 WORDS) |
