Kinetics of Mn3+–Oxalate Formation and Decay in Reactions Catalyzed by Manganese Peroxidase ofCeriporiopsis subvermispora

The kinetics of Mn3+–oxalate formation and decay were investigated in reactions catalyzed by manganese peroxidase (MnP) from the basiomyceteCeriporiopsis subvermisporain the absence of externally added hydrogen peroxide. A characteristic lag observed in the formation of this complex was shortened by glyoxylate or catalytic amounts of Mn3+or hydrogen peroxide. MnP titers had a minor effect on this lag and did not influence the decay rate of the complex. In contrast, Mn2+and oxalate drastically affected maximal concentrations of the Mn3+–oxalate complex formed, the decay of which was accelerated at high Mn2+levels. The highest concentration of complex was obtained at pH 4.0, whereas an inverse relationship was found between the pH of the reaction and the decay rate of the complex with MnP present. In the absence of MnP, the best fit for the decay kinetics of the complex gave an order of 3/2 at concentrations in the range of 30–100 μM, with akobs= 0.012 min−1M−0.5at pH 4.0. The rate constant increases at lower pH values and decreases at high oxalate concentrations. The physiological relevance of these findings is discussed.