title: Active labeling of phosphatidylcholines by [1-14C]docosahexaenoate in isolated photoreceptor membranes.
abstract: Isolated bovine rod outer segments and photoreceptor disks actively incorporated [1-14C]docosahexaenoate (22:6) into phospholipids when incubated in the presence of CoA, ATP, and Mg2+. About 80% of the esterified fatty acid was in phosphatidylcholine (PC). Microsomal and mitochondrial fractions incorporated as much 22:6 as rod outer segments, but it was distributed among various phospholipids and neutral glycerides. The isolated photoreceptor membrane thus contains an acyl-CoA synthetase which activates the fatty acid and a docosahexaenoyl-CoA-lysophosphatidylcholine acyltransferase activity. The specific radioactivity of PC was higher in rod outer segments than in the other subcellular fractions. About 2/3 of the label in photoreceptor membrane PC was in its dipolyunsaturated molecular species and 1/3 in hexaenes. Dipolyunsaturated PCs showed high turnover rates of 22:6 in all three subcellular membranes, especially in mitochondria. Retinal membranes in vitro seem to take up free [14C]22:6 from the medium by simple diffusion or partition into the membrane lipid. The ability of these membranes to activate and esterify [1-14C]22:6 indicates that docosahexaenoate-containing molecular species of retina lipids, including those of photoreceptor membranes, are subject to acylation-deacylation reactions in situ.
mesh_terms: D000818:Animals; D002417:Cattle; D004281:Docosahexaenoic Acids; D005227:Fatty Acids / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D010786:Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism*
chemical_list: D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D010743:Phospholipids; D004281:Docosahexaenoic Acids