Docosahexaenoyl Chains are Introduced in Phosphatidic Acid During De Novo Synthesis in Retinal Microsomes

Abstract

Phosphatidic acid from microsomal membranes of bovine retina contains 21% of docosahexaenoate. If entire retinas are incubated during short-periods of time with dl-propranolol about a fourfold increase takes place in the content of microsomal phosphatidic acid. Moreover docosahexaenoate as well as other acyl chains are increased. It is suggested that a significative proportion of docosahexaenoyl groups of other phospholipids is introduced into the glycerolipids during the de novo biosynthesis of phospatidic acid in the endoplasmic reticulum. Diacylglycerol of the toad retina is highly enriched in docosahexaenoate and has been implicated to have a biosynthetic origin, Howeverm bovine retina diacylglycerols contain relatively low proportions of this fatty acid. This may indicate either that there is a mixture of several diacylglycerols with different fatty acid profiles or that the docosahexaenoate enriched phospatidic acid is metabolized without conversion into diacylglycerols. The alternative pathway investigated at present is docosahexaenoate containing phsophatidylserine synthesis from phosphatidic acid without involving base exchange reaction. When using 2-³H-glycerol as a marker of the de novo synthesis we obtained evidence of a rapid phosphatidic acid formation. A route introducing docosahexaenoate during phosphatidic acid synthesis may actively participate in controlling membrane function by changing membrane fluidity.