Steady-state kinetics of lipoxygenase oxygenation of unsaturated fatty acids.

The oxygenation of linoleate and arachidonate catalyzed by soybean lipoxygenase is subject to competitive product inhibition. For normal conditions, there is an additional inhibition due to product that causes the reaction to cease before completion. This process is reversible upon addition of further substrate and is proposed to be a chemical (reversible) change of the enzyme. At very low enzyme concentrations, inactivation or adsorption of enzyme on the vessel surface (or "wall effect") is significant, leading to even lower rates and percent completions. In the very early stages of a typical catalyzed reaction, a lag, or induction period, occurs. It was previously known that this lag is eliminated by product hydroperoxide--and not by the corresponding alcohol. The hydroperoxide elimination of the lag is inhibited by the alcohol. It is proposed that this is a chemical activation of the enzyme to produce a catalytically functional form.