EFFECTS OF MN2+ AND OXALATE ON THE CATALYTIC ACTIVITY OF MANGANESE PEROXIDASE

Manganese peroxidase from Phanerochaete chrysosporium is an extracellu lar 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 che lator is not included. The catalatic activity was observed in the pH r ange 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 2 5 degrees C. Oxalate inhibited oxygen production by increasing the app arent K-m for Mn2+ for catalatic activity from micromolar to millimola r 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 h ydrogen peroxide in an environment where free oxalate may be limited. (C) 1997 Academic Press.