Further studies of the kinetics of oxygenation of arachidonic acid by soybean lipoxygenase.

A kinetic model for soybean lipoxygenase (EC 1.13.11.12) has been examined by comparing results from extensive experimental data with theoretical data generated from a computer program. Kinetic constants have been established by closely fitting experimental and computer-generated data with both product formation versus time, and the more complex accelerative and decelerative relationships of velocity changes with time. It has been confirmed that activation of lipoxygenase by its hydroperoxide product is necessary for activity, and product removal gives inhibition in a manner quantitatively predicted by the model. The earliest accurate measurement of velocity (at 9 s) is a convenient index of the amount of product-activator present in reaction mixtures, and can be used to assay quantitatively the amount of product-activator. The results confirm that soybean lipoxygenase catalyzes a product-activated, substrate-inhibited oxygenation accompanied by a self-catalyzed destruction of its activity.