Effects of Mn2+ and oxalate on the catalatic activity of manganese peroxidase.

Manganese peroxidase from Phanerochaete chrysosporium is an extracellular heme-containing enzyme known to catalyze the oxidation of Mn2+ to Mn3+ in a reaction requiring oxalate or another appropriate manganese chelator. We have found that the enzyme can also catalyze a manganese-dependent disproportionation of hydrogen peroxide when a manganese chelator is not included. The catalatic activity was observed in the pH range from 3.0 to 8.5, and the apparent second-order rate constant for catalatic reaction was about 2 x 10(5) M-1 s-1 at pH 4.5 to 7.0 at 25 degrees C. Oxalate inhibited oxygen production by increasing the apparent K(m) for Mn2+ for catalatic activity from micromolar to millimolar levels and facilitating peroxidase activity. Catalase-type function was recovered by excess of Mn2+ in the presence of oxalate. We propose that catalatic activity may protect the enzyme from inactivation by hydrogen peroxide in an environment where free oxalate may be limited.