BISTABILITY AND REACTION THRESHOLDS IN THE PHENOL-INHIBITED PEROXIDASE-CATALYZED OXIDATION OF INDOLE-3-ACETIC-ACID

A model mechanism for the phenol-inhibited peroxidase-catalyzed oxidat ion of indole-3-acetic acid (IAA) is proposed and analyzed. The model involves an autocatalytic free radical species that sustains IAA oxida tion and the phenolic inhibitor acting as a free radical scavenger. Un der a fixed set of parameter values, the model exhibits a coexistence of two stable steady states. This bistability phenomenon explains the origin of the experimentally observed threshold inhibitor concentratio ns above which IAA oxidation stops. The variation of the inhibitor thr eshold level with enzyme and substrate concentrations are reproduced b y the model almost quantitatively.