OXIDATION OF LINOLEYL ALCOHOL BY POTATO-TUBER LIPOXYGENASE - POSSIBLEMECHANISM AND THE ROLE OF CARBOXYLIC GROUP IN SUBSTRATE-BINDING

We have studied the aerobic oxidation of linoleyl alcohol (LAL) by pot ato tuber Lipoxygenase in the presence of 0.02% (w/v) non-ionic deterg ent Lubrol PX (and its analog C12E10) and 0.1 mM sodium dodecyl sulfat e to investigate the role of carboxylic group in substrate binding. Wh ile the enzyme displayed a comparable affinity toward LA and LAL, the rate of LAL oxidation was approximately one-fourth of that of linoleic acid. The pH-profile of the reaction suggests that the rate of LAL ox idation is controlled by two ionizable groups with pK(a) values of 5.3 and 7.5, with optimal pH being 6.4 +/- 0.1. Since LAL is not ionizabl e at this pH, we conclude that the rate of the reaction is controlled by two ionogenic groups of the enzyme. The primary dioxygenation produ ct(s) of LAL had a maximal absorbance at 233 +/- 1 nm. The products ha ve been isolated, catalytically hydrogenated with H-2 over Pd on carbo n, and analyzed by GC-MS. Two major equimolar products were found to b e 9- and 13-hydroxystearyl alcohols, indicating that 9- and 13-hydrope roxylinoleyl alcohols are the primary dioxygenation products. Based on these results we propose that the carboxyl group of polyunsaturated f atty acid may not be involved in substrate binding of potato tuber lip oxygenase. (C) 1998 Academic Press.