Abstract
The activity of calcium-stimulated microsomal phospholipase towards endogenous membrane bound phospholipids was monitored by analyzing the fatty acids released using gas chromatography. Activation by calcium (10 mM) resulted in the release of 2.1 nmoles fatty acid/10 mg microsomal protein/hr. The pattern of release of particular fatty acids reflected their concentration in the microsomal phospholipids. The effects of feeding 10 and 50% dietary linoelaidate (t,t18:2) and hydrogenated tallow (i.e., essential fatty acid deficient) on microsomal fatty acids and phospholipase activity was determined. The levels of t,t18:2 in the microsomal phospholipids increased with dietary intake and duration of feeding and attained 8.4% of total fatty acids after 11 weeks. There was a concomitant increase in linoleic acid and a decrease in arachidonic acid levels in microsomal lipids. The microsomal phospholipids of animals receiving exclusively hydrogenated tallow contained only trace amounts of linoleic and arachidonic acid after four weeks. The amount of eicosatrienoic acid increased dramatically in these animals. Palmitoleic and oleic acid also increased. The calcium-stimulated phospholipase activity in liver microsomes was unchanged by alterations in the fatty acid composition of the phospholipids.
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