Nonlinear dynamics of the peroxidase-oxidase reaction: I. Bistability and bursting oscillations at low enzyme concentrations

Under CSTR or semibatch conditions, the horseradish peroxidase (HRP)-cataly zed peroxidase-oxidase (PO) reaction evidences a wide range of nonlinear dy namical behaviors. Many of these regimes have proved to be predictable by a detailed model of the reaction first proposed in 1995. This model, which w e refer to as BFSO, can also account for experimentally observed bifurcatio n sequences in response to varying concentrations of phenolic modifiers and rates of hydrogen donor input. Among those findings for which the model ca nnot account is the observation of bistability and bursting at low enzyme c oncentrations. This deficiency is important not only because these phenomen a are biologically important but also because their existence requires a to pology which, for the experimental circumstances in question, appears to be inconsistent with the model as originally formulated. In the present paper , we show that this deficiency can be remedied by the inclusion of an addit ional reaction whereby NADH and superoxide anion react in the presence of h ydrogen ion to produce WAD radicals and hydrogen peroxide. Comparison of th e modified model's behavior with laboratory experiments suggests semiquanti tative agreement between theory and observation. In particular, the model i s able to reproduce experimentally observed responses to short-term perturb ation by oxygen input suspension and the addition of hydrogen peroxide to t he reaction mixture, as well as what was first described as "autonomous" sw itching between stable and oscillatory dynamics. Mathematically, addition o f the new reaction makes possible the interaction of Hopf and hysteresis in stabilities, as previously described in the Belousov-Zhabotinski reaction.