Excess substrate inhibition of soybean lipoxygenase-1 is mainly oxygen-dependent.

Soybean lipoxygenase-1 kinetics are known to show product and substrate inhibition. With linoleic acid as the substrate and using a simple Michaelis-Menten formulation, we have shown that K(ss), the substrate inhibition constant was increased by more than five-fold when initial oxygen concentration was increased from 228 to 1140 microM. Excess substrate inhibition is in fact almost avoided at high initial oxygen concentration. This modification seems correlated with enzyme saturation with oxygen relative to linoleic acid, as reflected by alterations of the substrate conversion rate. Possible implications for the enzyme kinetics are discussed.