Enzymic characterization of epidermis-derived 12-lipoxygenase isoenzymes

Substrate selectivity and other enzymic characteristics of two epidermis-de rived lipoxygenases (LOXs), the epidermis-type (e) (12S)-LOX and (12R)-LOX, were compared with those of the platelet-type (p) (12S)-LOX. In contrast w ith p(12S)-LOX, e(12S)-LOX and (12R)-LOX exhibited no or very low reactivit y towards the customary substrates linoleic acid and arachidonic acid but m etabolized the corresponding fatty acid methyl esters, which, in contrast, were not accepted as substrates by p(12S)LOX. Other esters of arachidonic a cid and linoleic acid, including propan-2-yl and cholesterol esters, 1-palm itoyl-2-arachidonyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-linoleyl-sn- glycero-3-phosphoethanolamine, and ceramide 1 carrying an omega -linoleic a cid ester, were not metabolized by these three LOX isoenzymes. Among variou s polyunsaturated fatty acids the isomeric eico-satrienoic acids were found to be oxygenated by e(12S)-LOX but not by (12R)-LOX. 4,7,10,13,16,19-Docos ahexaenoic acid as a substrate was restricted to p(12S)-LOX. Variations in the pH and the Ca2+ content of the incubation medium affected the catalytic potential only slightly. Whereas (12R)-LOX activity increased in the prese nce of Ca2+ and with an acidic pH, Ca2+ had no effect on p(12S)-LOX and e(1 2S)-LOX: an acidic pH decreased the catalytic activity of the latter two. H owever, the catalytic activity of the epidermis-type isoenzymes, but not of p(12S)-LOX, was found to be markedly increased in the presence of DMSO. Un der these conditions, e(12S)-LOX and (12R)-LOX oxygenated 4,7,10,13,16,19-d ocosahexaenoic acid to 14-hydroxy-4,7,10,12,16, 19-docosahexaenoic acid and 13-hydroxy-4,7,10,14,16,19-docosahexaenoic acid respectively. In addition, (9R)-hydroxyoctadeca-10,12-dienoic acid methyl ester was generated from li noleic acid methyl ester by (12R)-LOX. Independently of the substrate, the catalytic activity of e(12S)-LOX and (12R)-LOX was always at most 2%, of th at of p(12S)-LOX with arachidonic acid as substrate.