THE EFFECT OF MANGANESE ON THE OXIDATION OF CHEMICALS BY LIGNIN PEROXIDASE

It has recently been discovered that lignin peroxidase isozyme H2 (LiP H2) has the ability to oxidize Mn2+ (Khindaria et al., 1995). Furtherm ore, at pH 4.5, the physiological pH of Phanerochaete chrysosporium, L iPH2 oxidizes Mn2+ at a much faster rate (25 times) than veratryl alco hol (VA). The ability of Mn2+ to act as a redox mediator for indirect oxidations catalyzed by LiPH2 was therefore investigated. In the prese nce of physiologically relevant levels of oxalate and Mn2+, the rate o f LiPH2-catalyzed oxidation of all substrates studied was dramatically increased. Up to 10-fold stimulations were observed compared to the r ates of oxidation of substrate in either the presence or absence of VA . We propose that the stimulation is due to the ability of LiPH2 to ox idize Mn2+, producing th@ strong oxidant Mn3+, at a high rate. The rat es of oxidation of the substrates showed a hyperbolic dependence on Mn 2+ in the presence of oxalate, a chelator which was required for maxim al activity. The oxalate dependence of the oxidation rates correlated well with the concentration of the 1:1 complex of Mn2+-oxalate. The re lative concentrations of the substrates and H2O2 and the rate constant s for their reactions with Mn3+ determined which chemical was oxidized by the enzymatically produced Mn3+. The importance of the ability of Mn2+-oxalate to stimulate the oxidation of chemicals by LiPH2, is disc ussed.