Cytochrome cb-type nitric oxide reductase with cytochrome c oxidase activity from Paracoccus denitrificans ATCC 35512

Abstract

A highly active nitric oxide reductase was purified from Paracoccus denitrificans ATCC 35512, formerly named Thiosphaera pantotropha, which was anaerobically cultivated in the presence of nitrate. The enzyme was composed of two subunits with molecular masses of 34 and 15 kDa and contained two hemes b and one heme c per molecule. Copper was not found in the enzyme. The spectral properties suggested that one of the two hemes b and heme c were in six-coordinated low-spin states and another heme b was in a five-coordinated high-spin state and reacted with carbon monoxide. The enzyme showed high cytochrome c-nitric oxide oxidoreductase activity and formed nitrous oxide from nitric oxide with the expected stoichiometry when P. denitrificans ATCC 35512 ferrocytochrome c-550 was used as the electron donor. The V(max) and K(m) values for nitric oxide were 84 μmol of nitric oxide per min/mg of protein and 0.25 μM, respectively. Furthermore, the enzyme showed ferrocytochrome c-550-O2 oxidoreductase activity with a V(max) of 8.4 μmol of O2 per min/mg of protein and a K(m) value of 0.9 mM. Both activities were 50% inhibited by about 0.3 mM KCN.