Metabolism of 1-acyl-2-oleoyl-sn-glycero-3-phosphoethanolamine in castor oil biosynthesis

We have examined the role of 2-oleoyl-PE (phosphatidylethanolamine) in the biosynthesis of triacylglycerols (TAG) by castor microsomes. In castor micr osomal incubation, the label from C-14-oleate of 1-palmitoyl-2-[1-C-14]oleo yl-sn-glycero-3-phosphoethanolamine is incorporated into TAG containing ric inoleate. The enzyme characteristics, such as optimal pH, and the effect of incubation components of the oleoyl-12-hydroxylase using 2-oleoyl-PE as in cubation substrate are similar to those for 2-oleoyl-PC (phosphatidylcholin e). However, compared to 2-oleoyl-PC, 2-oleoyl-PE is a less efficient incub ation substrate of oleoyl-12-hydroxylase in castor microsomes. Unlike 2-ole oyl-PC, 2-oleoyl-PE is not hydroxylated to 2-ricin-oleoyl-PE by oleoyl-12-h ydroxylase and is not desaturated to 2-linoleoyl-PE by oleoyl-12-desaturase . We have demonstrated the conversion of 2-oleoyl-PE to 2-oleoyl-PC and vic e versa. The incorporation of label from 2-[C-14]oleoyl-PE into TAC occurs after its conversion to 2-oleoyl-PC, which can then be hydroxylated or desa turated. We detected neither PE-N-monomethyl nor PE-N,N-dimethyl, the inter mediates from PE to PC by N-methylation. The conversion of 2-oleoyl-PE to 2 -oleoyl-PC likely occurs via hydrolysis to 1,2-diacyl-sn- glycerol by phosp holipase C and then by cholinephosphotransferase. This conversion does not appear to play a key role in driving ricinoleate into TAG.