Cytochrome c peroxidase from Methylococcus capsulatus Bath

Abstract

A bacterial cytochrome c peroxidase was purified from the obligate methanotroph Methylococcus capsulatus Bath in either the fully oxidized or the half reduced form depending on the purification procedure. The cytochrome was a homo-dimer with a subunit mol mass of 35.8 kDa and an isoelectric point of 4.5. At physiological temperatures, the enzyme contained one high-spin, low-potential (E _m7 = –254 mV) and one low-spin, high-potential (E _m7 = +432 mM ) heme. The low-potential heme center exhibited a spin-state transition from the penta-coordinated, high-spin configuration to a low-spin configuration upon cooling the enzyme to cryogenic temperatures. Using M. capsulatus Bath ferrocytochrome c ₅₅₅ as the electron donor, the K _M and V _max for peroxide reduction were 510 ± 100 nM and 425 ± 22 mol ferrocytochrome c ₅₅₅ oxidized min^–1 (mole cytochrome c peroxidase)^–1, respectively.