Positional specificity in the incorporation of isomericcis- andtrans-octadecenoic acids into glycerolipids of cultured soya cells

摘要

Heterotrophically grown cell suspension cultures of soya (Glycine maxL.) were incubated with two different mixed substrates consisting of positional isomers of eithercis-1-14Coctadecenoic acids (Δ8 to δ15) ortrans-1-14Coctadecenoic acids (Δ8 to Δ16), each with known composition. With both substrates, about one-fourth of the radioactivity supplied was incorporated into the diacylglycerophosphocholines, while another one-fourth of the radioactivity was almost equally distributed between diacylglycerophos-phoethanolamines and triacylglycerols. All the positional isomers ofcis-andtrans-octadecenoic acids supplied to the cells were readily incorporated into various classes of glycerolipids. None of the octadecenoic acids was isomerized, elongated or desaturated during incubation. From thecis-octadecenoic acids, only the naturally occurring Δ9-isomer (oleic acid) was preferentially incorporated into position 2 of diacylglycerophosphocholines, diacylglycerophospho-ethanolamines, and triacyglycerols; all the other isomers exhibited a strong affinity for position 1 of the glycerophospholipids and positions 1 and 3 of the triacylglycerols. From thetrans-octadecenoic acids, only the Δ9-isomer (elaidic acid) was preferentially incorporated into position 2 of diacylglycerophospho-cholines and triacylglycerols; all the other isomers preferred position 1 and positions 1 and 3, respectively, of these lipids. In diacylglycerophospho-ethanolamines, however, each of thetrans-octadecenoic acids, including the Δ9-isomer, exhibited a strong affinity for position 1. Apparently, the enzymes involved in the incorporation of exogenous monounsaturated fatty acids into membrane lipids of plant cells can recognize the preferred substrate in a mixture of closely related i