Endoplasmic oleoyl-PC desaturase references the second double bond

Abstract

The regiospecificity for the gene product of fad2, 1 1 We will employ the convention of using fad2 for the gene and oleoyl-PC desaturase or FAD2 for the gene product. This permits us to avoid describing the enzyme as a Δ 12 desaturase, or an ω-6 desaturase. The latter designations involve an assertion about the substrate specificity no longer tenable based on this work. PC is the abbreviation for phosphatidylcholine, the most important phospholipid substrate for this activity. GLC is gas-liquid chromatography. GC/MS spectroscopy is separation by capillary gas chromatography with mass spectral, electron-impact detection. 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.