Biosynthesis of docosahexaenoate-containing glycerolipid molecular speciesin the retina

Vertebrate retinas are highly enriched in long-chain polyunsaturated fatty acids (PUFA), especially docosahexaenoic acid (22:6n-3, DHA). In the presen t study, we investigated the role of de novo, synthesis in the enrichment o f 22:6n-3 in characteristic molecular species of retinal glycerolipids. Fol lowing the incubation of fresh dark-adapted retinas with [2-H-3]-glycerol, individual glycerolipids were isolated and converted into either diacylglyc erol acetates (DGAC) or diacylglycerol benzoates (DGBZ), followed by high-p erformance liquid chromatography (HPLC) and flow-through radioactivity dete ction. Total lipids from rat retinas incubated with [SH]-glycerol were anal yzed. Unlike what was observed with frog retinas, relative larger of amount s of di-22:6 molecular species were synthesized de novo. In both rat and fr og retinas, there was synthesis of glycerolipid molecular species containin g two PUFA tone of which was 22:6) in larger amounts than predicted by thei r steady-state mass levels. These results demonstrate that the unique molec ular species of retinal glycerolipids are derived only in part through de n ovo synthesis, but that molecular rearrangement (remodeling) and differenti al turnover must also play a role in maintaining the high levels of 22:6 fo und in rod phohtoreceptor outer segments (ROS) membranes.