Regulation of selectivity of CDPcholine: 1,2-diacyl-sn-glycerol cholinephosphotransferase in rat liver microsomes towards different molecular species of 1,2-diacyl-sn -glycerols

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Abstract
The suitability of monoenoic, dienoic, tetraenoic and hexaenoic molecular species of 1,2-diacyl-sn-glycerols as substrates for the CDPcholine: 1,2-diacyl-sn-glycerol cholinephosphotransferase (EC 2.7.8.2) was studied in rat liver microsomes. No statistically significant difference in rates of phosphatidylcholine synthesis with various diacylglycerols was found at 0.4 mM, although a moderate discrimination against hexaenoic species relative to monoenoic and dienoic species was observed at 0.25 mM. Addition of palmitoyl-CoA (7.5 .mu.M) significantly enhanced cholinephosphotransferase activity when tetraenoic diacylglycerols were added at 0.25 or 0.40 mM. CDPethanolamine at 24.4 .mu.M apparently inhibited rates of phosphatidylcholine biosynthesis by 54 and 39% with hexaenoic and monoenoic 1,2-diacyl-sn-glycerols, respectively, whereas no significant effects were observed in the case of dienoic and tetraenoic species. These findings may partially explain why 1-saturated 2-docosahexaenoyl diacylglycerols are used to a greater extent for phosphatidylethanolamine than for phosphatidylcholine synthesis in rat liver in vivo. The selectivity of the cholinephosphotransferase for certain molecular species of 1,2-diacyl-sn-glycerols is apparently a function of diacylglycerol concentration and may be mediated under physiological conditions by substrates for enzymes which compete for common diacylglycerol precursors.