The NADH oxidation catalyzed by horseradish peroxidase is well known to produce oscillations in an open system with diffusion of oxygen. We propose here a model based on a cycle between two oxidation states of the enzyme. The two reactions of the cycle are auto-catalytic and produce a free radical intermediate, but one consumes oxygen. Because of the enzyme cycle, this model is reduced to three independent species. The model can be studied with normal mode stability analysis. The results of this analysis predict that in some cases the steady state should be unstable with an oscillatory behavior. Then the numerical simulations show that sustained oscillations are exhibited by our model. The shape of these oscillations are very similar to those obtained experimentally (I. Yamazaki and K. Yokota, Mol. Cell Biol., 2 (1973) 39). © 1991.
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