EXCESS SUBSTRATE-INHIBITION OF SOYBEAN LIPOXYGENASE-1 IS MAINLY OXYGEN-DEPENDENT

Soybean lipoxygenase-1 kinetics are known to show product and substrat e inhibition, With linoleic acid as the substrate and using a simple M ichaelis-Menten formulation, we have shown that K-ss, the substrate in hibition constant was increased by more than five-fold when initial ox ygen concentration was increased from 228 to 1140 mu M. Excess substra te inhibition is in fact almost avoided at high initial oxygen concent ration, 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 kineti cs are discussed. (C) 1997 Federation of European Biochemical Societie s.