Mechanism of protection of peroxidase activity by oscillatory dynamics

Abstract

The peroxidase-oxidase reaction is known to involve reactive oxygen species as intermediates. These intermediates inactivate many types of biomolecules, including peroxidase itself. Previously, we have shown that oscillatory dynamics in the peroxidase-oxidase reaction seem to protect the enzyme from inactivation. It was suggested that this is due to a lower average concentration of reactive oxygen species in the oscillatory state compared to the steady state. Here, we studied the peroxidase-oxidase reaction with either 4-hydroxybenzoic acid or melatonin as cofactors. We show that the protective effect of oscillatory dynamics is present in both cases. We also found that the enzyme degradation depends on the concentration of the cofactor and on the pH of the reaction mixture. We simulated the oscillatory behaviour, including the oscillation/steady state bistability observed experimentally, using a detailed reaction scheme. The computational results confirm the hypothesis that protection is due to lower average concentrations of superoxide radical during oscillations. They also show that the shape of the oscillations changes with increasing cofactor concentration resulting in a further decrease in the average concentration of radicals. We therefore hypothesize that the protective effect of oscillatory dynamics is a general effect in this system. Keywords: peroxidase; superoxide radical; hydrogen peroxide; oscillations; enzyme degradation.Within the last 30 years the number of reports on oscillating biochemical processes has grown considerably [1]. From the first observations of oscillations in glycolysis in yeast and muscle cells [2,3] through measurements of oscillations in secondary messengers such as cyclic AMP [4] and cytosolic Ca 2+ [5] to recent observations of oscillations in intracellular NAD(P)H, pH, hydrogen peroxide, and superoxide in migrating neutrophils [6,7] we are beginning to understand that temporal behaviours, that is dynamics, play important roles in cell metabolism. Thus, it might be appropriate to suggest that in addition to its genome and proteome a given cell should also be characterized by the diversity of its dynamic behaviours.In spite of their universal occurrence the functions of metabolic oscillations in cells are still not well understood. It is not certain whether some biochemical oscillations occur as harmless side-effects of the nonlinear properties of metabolic enzymes or whether they always serve one or more important functions. Over the years many different roles have been proposed for oscillations. It has been suggested that they provide metabolism with an increased thermodynamic efficiency [8]. Furthermore, oscillations, e.g. those of second messengers such as calcium ions, are believed to have information stored in their frequency [9]. Roles as biological time-keepers [1] and encoders of transmembrane signalling have also been proposed [10]. Presumably, oscillations serve many functions in cell metabolism. Here we wish to explore further another potential role of oscillating...

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