Abstract: The substrate inhibition was observed in the hydroperoxidation of linoleic acid catalyzed by soybean lipoxygenase at substrate concentrations higher than 0.075 mmol/L. Addition of DMF(lgP=1.01) could raise the substrate level to 232 mmol/L, and increase the hydroperoxide(HPOD) yield from 38.93% to 66.09%. The results of lyophilization test show that DMF mixed with substrate didn't influence on the enzymatic activity evidently although DMF made the enzymatic activity declined obviously in the absence of substrate. For lipoxygenase DMF served as either an activator at lower level or an inhibitor at higher level, which was illustrated by the activation constant K_a, the inhibition constant K_i and the effect of DMF with substrate on enzymatic activity. The substrate inhibition constant K_ss at higher DMF level increased by 1000—5600 folds, which implied that the interaction between relaxation of substrate inhibition and competitive inhibition of lipoxygenase resulted from DMF made the excess substrate inhibition greatly released. The maximum K_ss and K_i obtained at 5% DMF means that the maximum relaxation of substrate inhibition and the minimum competitive inhibition to lipoxygenase appeared simultaneously.

Key words: Lipoxygenase, Substrate inhibition, Enzyme, N,N-Dimethylformamide, Linoleic acid