A new iron oxidase from a moderately thermophilic iron oxidizing bacterium strain TI-1

Iron oxidase was purified from plasma membranes of a moderately thermophilic iron oxidizing bacterium strain TI-1 in an electrophoretically homogenous state. Spectrum analyses of purified enzyme showed the existence of cytochrome a, but not cytochrome b and c types. Iron oxidase was composed of five subunits with apparent molecular masses of 46 kDa (α), 28 kDa (β), 24 kDa (γ), 20 kDa (δ), and 17 kDa (ε). As the molecular mass of a native enzyme was estimated to be 263 kDa in the presence of 0.1% n-dodecyl-β-D-maltopyranoside (DM), a native iron oxidase purified from strain TI-1 seems to be a homodimeric enzyme (αβγδε)₂. Optimum pH and temperature for iron oxidation were pH 3.0 and 45°C, respectively. The K_m of iron oxidase for Fe²⁺ was 1.06 mM and V_max for O₂ uptake was 13.8 μmol·mg^-1·min^-1. The activity was strongly inhibited by cyanide and azide. Purified enzyme from strain TI-1 is a new iron oxidase in which electrons of Fe²⁺ were transferred to haem a and then to the molecular oxygen.