The catalase activity of Nα‐acetyl‐microperoxidase‐8

Abstract: N ^α ‐Acetylated microperoxidase‐8 (Ac‐MP‐8) is a water soluble, ferric heme model for peroxidases. We report here that Ac‐MP‐8 catalyzes catalase‐type reaction in addition to peroxidase‐type and cytochrome P450‐type reactions. The catalase activity of Ac‐MP‐8 was determined by the Clark oxygen electrode, which measures the production of oxygen in solution. The K_m and k_cat of the decomposition of hydrogen peroxide (H₂O₂) catalyzed by Ac‐MP‐8 are 40.9 mm and 4.1 per s, respectively. The specificity constant (k_cat/K_m) of Ac‐MP‐8 in catalase‐type reaction of H₂O₂ is 100.2,/m /s, which is 5‐ to 12‐ and 50‐ to 100‐fold less than those of MPs in cytochrome P450‐type reaction of aniline/H₂O₂ and peroxidase‐type reaction of o‐methoxyphenol/H₂O₂, respectively. These results indicate that Ac‐MP‐8 can catalyze three different types of reactions, and the relative catalytic specificities of Ac‐MP‐8 with a histidyl ligand exhibit the following orders: peroxidase‐type > cytochrome P450‐type > catalase‐type reactions. Comparisons of the enzyme activities of Ac‐MP‐8 suggest that the fifth ligands of hemoproteins influence the ratio of the three types of reactions.