Kinetic analysis of the action of soybean lipoxygenase on linoleic acid

The time course of the soybean lipoxygenase-catalyzed oxygenation of linoleic acid has been analyzed using a kinetic scheme based on two binding sites, compulsory product activation and competitive inhibition by substrate and by product. The dissociation constant (Kp) of the product from the free enzyme is much smaller than 10(-5) M, the dissociation constant of the substrate from the enzyme-substrate-product complex (Kps) has a value of (7.7 +/- 0.3) x 10(-6) M, and the competitive inhibitors constant of the product (Kpp) is equal to (2.9 +/- 0.3) x 10(-5) M Reduction of the hydroperoxide product to a hydroxy acid by sodium borohydride does not alter the product activation kinetics. From the study of the time course of the reaction, no evidence was found for the irreversible inactivation of the enzyme.