Substrate-selectivity of rat liver microsomal 1,2-diacylglycerol: CDP-choline(ethanolamine)...

Rat liver microsomes containing 1,2-diacylglycerols formed from the endogenous phosphatidycholines by the action of 1,2-diacylglycerol: CDPcholine cholinephosphotransferase (E.C. 2.7.8.2.) were used as a source of enzymes and substrates. A marked selectivity of 1,2-diacylglycerol: CDPethanolamine ethanolaminephosphotransferase (E.C. 2.7.8.1.) was revealed for utilizing endogenous hexaenoic diaglycerol, while cholinephosphotransferase utilized without marked selectivity the endogenous 1,2-diacylglycerol species differing in the degree of unsaturation. By using microsomes prepared after injecting the animals with 1-acyl lysophosphatidylcholines labeled with radioactive myristic, palmitic, and stearic acids, the selectivity of the transferases towards the saturated fatty acids in the 1-position of the endogenous substrates was studied. In incubation of the labeled microsomes with CMP, cholinephosphotransferase appeared to utilize 1-myristyl phosphatidylcholine most rapidly and, in decreasing order, the 1-palmityl and 1-stearyl species. Ethanolaminephosphotransferase utilized the endogenous 1-stearyl diacylglycerol in preference to 1-palmityl type.