Docosahexaenoic,arachidonic, palmitic,and oleic acids are differentially esterified into phospholipids of frog retina

Docosahexaenoic acid (22:6n-3) is highly enriched in the retina. To determine if retinal cells take up and metabolize fatty acids in a specific manner, retinas from Rana pipiens were incubated for 3 h with an equimolar mixture of tritiated 22:6n-3, arachidonic acid (20:4n-6), palmitic acid, and oleic acid. The radiolabeling of retinal lipids was determined and compared to the endogenous fatty acid content of the lipids. The results showed that in most, but not all, cases, the relative labeling with the four precursor fatty acids was similar to their relative abundance in each glycerolipid. Thus, during retinal glycerolipid synthesis, either through de novo or acyl exchange reactions, fatty acids are incorporated in proportions reflecting their steady-state mass levels. Since other studies with labeled glycerol have shown greater differences between early labeling patterns and molecular species mass, the final incorporation we report may be due primarily to acyl exchange reactions.