COMPETITIVE-INHIBITION OF THE 5-LIPOXYGENASE-CATALYZED LINOLEATE OXIDATION BY ARACHIDONIC AND 5-HYDROPEROXY-EICOSATETRAENOIC ACIDS

Linoleic and arachidonic acids are competing substrates for 5-lipoxyge nase from barley. When these two substrates are added simultaneously, arachidonic acid acts as a competitive inhibitor of linoleic acid oxid ation with K-i of 20 mu M, the same value as the Michaelis constant fo r arachidonate oxygenation by this enzyme (22 +/- 3 mu M). Linoleic ac id hydroperoxide accumulated in the reaction mixture does not inhibit the enzymatic process, while ararhidonic acid hydroperoxy product (5-h ydroperoxy-6,8,11,14-eicosatetraenoic acid) inhibits it with very low K-i equal to 0.5 mu M.