A Comparison of Oleic Acid Metabolism in the Soybean ( Glycine max [L.] Merr.) Genotypes Williams and A5, a Mutant with Decreased Linoleic Acid in the Seed

Abstract

The metabolism of oleoyl coenzyme A (CoA) was examined in developing seed from two soybean (Glycine max [L.] Merr.) genotypes: Wil-liams, a standard cultivar and A5, a mutant containing nearly twice the oleic acid (18:1) content of Williams. The in vitro rates of esterification of oleoyl-CoA to lysophosphatides by acyl-CoA: lysophosphatidykcholine acyltransferase was similar in both genotypes and lysophosphatidyl-ethanolamine was a poor substrate. Crude extracts desaturated exogenous I1-'4Cjdioleoyl phosphatidylcholine at 14% of the rate achieved with 11-'4CIoleoyl-CoA, and 50 micromolar lysophosphatidylcholine. The desat-urase enzyme also required NADH for full activity. Extracts from Wil-liams contained 1.5-fold more oleoyl phosphatidylcholine desaturase activity, on a fresh weight basis, than did A5 and appeared to have a similar affinity for oleoyl-CoA. There was 1.2-to 1.9-fold more linoleic acid (18:2) in phosphatidylcholine from Williams than from A5, measured at two stages of development, but both genotypes had a similar distribution of fatty acids in the one and two positions. Phosphatidylethanolamine in A5 contained relatively more linoleic acid (18:2) in the one position than did Williams. The increased oleic acid (18:1) content in A5 appeared to be a result of decreased rates of 18:1 desaturation of oleoyl-phospha-tidylcholine in this genotype.