Initial incorporation into rat liver glycerolipids of intraportally injected [9,10- 3H 2]palmitic acid

Abstract

1. 1. [9,10- 3H 2]Palmitic acid complexed to serum albumin was injected intraportally into male rats. After 2–300 sec the livers were removed and the lipids were extracted. 2. 2. Labeled palmitic acid was rapidly incorporated into liver glycero-lipids. The amount of isotope in phosphatidic acids reached its maximum after 10–30 sec, and in diacylglycerols after 30–60 sec. In each lipid the turnover rates were the same for the main fractions of different degrees of unsaturation. 3. 3. In all diacylglycerolipids 90% of the incorporated [9,10- 3H 2]palmitic acid was located at position 1 as soon as 5 sec after injection. 4. 4. Most of the [9,10- 3H 2]palmitic acid incorporated into phosphatidylcholines and phosphatidylethanolamines by acylation of 2-acyl- sn-glycero-3-phosphorylcholine and 2-acyl-sw-glycero-3-phosphorylethanolamine was found in the tetraenoic fractions. With the exception of hexaenoic phosphatidylethanolamines, the highly unsaturated fractions received more palmitic acid by direct acylation reactions than by synthesis de novo. 5. 5. Diacylglycerols were randomly utilized for triacylglycerol biosynthesis. They were acylated by an acyl-CoA mixture which contained more highly unsaturated fatty acids than did position 3 of triacylglycerols.