MECHANISMS FOR PROTECTION AGAINST INACTIVATION OF MANGANESE PEROXIDASE BY HYDROGEN-PEROXIDE

It has been reported that cation radicals of aromatic substrates maint ain the active form of Lignin peroxidase by oxidatively converting com pound III, generated during peroxidase turnover, into ferric enzyme (D . P. Barr and S. D. Aust, 1994, Arch. Biochem Biophys. 312, 511-515). In this work, we investigated protective mechanisms for manganese pero xidase. Oxidation of Mn(II) by manganese peroxidase displayed complex kinetics, which were explained by accumulation of compound III followe d by its reactivation by the enzymatically produced Mn(III). Conversio n of compound III to ferric enzyme by Mn(III) was not observed for lig nin peroxidase or heme propionate-modified recombinant manganese perox idase, suggesting that Mn(III) may interact with compound III of nativ e manganese perorridase at a heme propionate to oxidize iron-coordinat ed superoxide via long-range electron transfer. Additionally, Mn(II) a lso reactivated compound III. Although this reaction was slower, it co uld prevent compound III accumulation when excess Mn(II) was present. Another protective mechanism for manganese peroxidase is proposed for insufficient chelator conditions. In contrast to effective Mn(II) chel ators, low-affinity ligands supported considerably slower enzyme turno ver, and Mn(III) released was more reactive with hydrogen peroxide, re sulting in a catalase-type reaction. Reactivation of compound III and catalatic activity may provide biologically relevant mechanisms for pr otection of manganese perorridase against suicidal inactivation by hyd rogen peroxide under a variety of manganese and oxalate conditions. (C ) 1998 Academic Press.