The steady-state kinetics of the oxygenation of linoleic acid catalysed by soybean lipoxygenase.

The steady-state kinetics of the oxygenation of linoleic acid catalysed by soybean lipoxygenase-1 were studied. The results showed that lipoxygenase-1 is strongly inhibited by its substrate, linoleic acid. In the presence of the product of the reaction, 13-LS-hydroperoxy-linoleic acid, the substrate inhibition only affects the apparent affinity for O2 and is of a hyperbolic type. A kinetic scheme of the oxygenation reaction is presented, which postulates two substrate-binding sites on the enzyme, one for linoleic acid and one for O2, and a regulatory binding site, which can either bind the product or the fatty acid substrate. Since previous studies indicated that the product of the reaction influences the oxidation state of the iron present in protein, the steady-state kinetics of the native enzyme and of the enzyme pre-incubated with the product were compared. Pre-incubation of the enzyme with the product did not lead to altered steady-state kinetics of the reaction compared to those of the native enzyme.