Kinetics of Mn3+-oxalate formation and decay in reactions catalyzed by manganese peroxidase of Ceriporiopsis subvermispora

The kinetics of Mn3+-oxalate formation and decay were investigated in react ions catalyzed by manganese peroxidase (MnP) from the basiomycete Ceriporio psis subvermispora in 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 concen trations of the Mn3+-oxalate complex formed, the decay of which was acceler ated 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 absenc e 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 mu M, with a k(obs) = 0.012 min(-1) M-0.5 at pH 4.0. The rate constant increases at lower pH values an d decreases at high oxalate concentrations. The physiological relevance of these findings is discussed. (C) 1998 Academic Press.