Endoplasmic oleoyl-PC desaturase references the second double bond

Abstract The regiospecificity for the gene product of fad2, 1 the microsomal oleoyl-PC desaturase from higher plants, differs from some previous suggestions. Rather than only referencing the carboxyl group (a Δ 12 desaturase) or the methyl terminus (an ω-6 desaturase), this desaturase locates the second double bond in its substrates by first referencing the existing double bond. This specificity was demonstrated for the oleoyl-PC desaturase cDNA from the developing seeds of peanut ( Arachis hypogaea L) expressed in yeast ( Saccharomyces cerevisae ). The expressed enzyme was capable of desaturating monounsaturated fatty acyl groups in membrane lipids. Endogenous palmitoleate was desaturated to cis , cis 9,12 hexadecadienoate (9( Z )12( Z )C16:2), endogenous oleate to linoleate (9( Z )12( Z ) octadecadienoate), and cis 10-nonadecenoate (provided as a supplement in the growth medium) to 10( Z )13( Z )C19:2. The rule, Δ x +3 where x =9 is the double bond location in the substrate, best describes the consistent placement of the second double bond in the above monounsaturated substrates for the oleoyl-PC desaturase of higher plants.