HIGH CONTENT OF 22-6 (DOCOSAHEXAENOATE) AND ACTIVE [2-H-3]-LABELED GLYCEROL METABOLISM OF PHOSPHATIDIC-ACID FROM PHOTORECEPTOR-MEMBRANES

The content, fatty acid composition and [2-3H]glycerol metabolism of phosphatidic acid of rod outer segment membranes from vertebrate retinas were studied. A relatively high content of phosphatidic acid was observed in rod outer segment membranes isolated from rat, toad and bovine retinas. In bovine retinas, .apprx. 65% of the acyl groups of phosphatidic acid were composed of docosahexaenoate. Arachidonate and docosapentaenoate represented .apprx. 4 and 5%, respectively, of the total, whereas stearate was the most common saturated acyl chain. An active [2-3H]glycerol metabolism in the phosphatidic acid of these membranes was found when whole retinas were incubated with the precursor for short periods prior to subcellular fractionation. The pool of phosphatidic acid enriched in docosahexaenoate may arise from de novo biosynthesis or from phospholipid degradation by a phospholipase D enzyme, and it may not be metabolically related, in any major fashion, to the diacylglycerols of rod outer segment membrane.