Endoplasmic oleoyl-PC desaturase references the second double bond

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 Delta (12) desaturase) o r the methyl terminus (an omega -6 desaturase), this desaturase locates the second double bond in its substrates by first referencing the existing dou ble bond. This specificity was demonstrated for the oleoyl-PC desaturase cD NA from the developing seeds of peanut (Arachis hypogaea L) expressed in ye ast (Saccharomyces cerevisae). The expressed enzyme was capable of desatura ting monounsaturated fatty acyl groups in membrane lipids. Endogenous palmi toleate 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-no nadecenoate (provided as a supplement in the growth medium) to 10(Z)13(Z)C1 9:2. The rule, Delta (x+3) where x=9 is the double bond location in the sub strate, best describes the consistent placement of the second double bond i n the above monounsaturated substrates for the oleoyl-PC desaturase of high er plants. (C) 2001 Elsevier Science Ltd. All rights reserved.