Studies with Clearing Factor IV. Fatty Acid Exchange Reaction Catalyzed by Clearing Factor.

It was previously reported (1) that postheparin Clearing Factor catalyzes the exchange of fatty acids with triglycerides, di-glycerides and monoglycerides. This exchange as measured by incorporation of C14 oleic acid, was postulated to take place only on the 1 and 3 position of the glyceride. It was thus suggested that the position specificity of Clearing Factor for the glyceride ester bonds was such that the exchange took place only in the 1, 3 positions. In these experiments no attempt was made to demonstrate that actual distribution of C14 fatty acids among the isomers of diglycerides and monoglycerides. These conclusions were rejected later by Korn(7). He used adipose tissue Clearing Factor and demonstrated random hydrolysis of fatty acids from various natural triglyc-erides and chylomicrons. These results were possibly affected by the presence of β-mono-glyceridase(8) and lipases other than the lipo-protein lipase in adipose tissue. Similar exchange reactions with C14 fatty acids and dibutyrine, catalyzed by adipose tissue lipoprotein lipase, were demonstrated (5). In this report, it was claimed that 2 to 8 carbon fatty acids were more readily incorporated in the 3-position of 1,2-dibutyr-ine and ester bonds were formed. On the other hand, with long chain fatty acids exchange reaction occurred only at C-1. The exchange reaction and hydrolysis had an optimum at pH 7 with an apparent increase of activity with increasing pH. The present report describes the exchange reaction of plasma Clearing Factor with C14 stearic and oleic acids and glyceride fractions of coconut oil and its hydrolysis products, i.e., 1,2- and 1,3-diglycerides, a- and β-monoglycerides. Methods and materials. The postheparin plasma Clearing Factor was prepared as previously reported (9). It had an activity of 16 μ E free fatty adds/ml postheparin plas-ma/hr. Stearic acid 1-C14, with a specific activity 21.4 mC/mM, and oleic acid-1-C14, 7.7 mC/mM were purchased from Volk isotopes.