Abstract
Roseobacter denitrificcans has a NO reductase (NOR) homologue that has cytochrome c-oxidase activity. The enzyme is composed of two subunits homologous to NorC and NorB of NOR from other bacterial species. They are encoded in an operon similar to nor gene clusters of Paracoccus denitrificans or Rhodobacter sphaeroides. However, the NOR homologue from R. denitrificans contains copper, while NOR has iron as the non-heme metal in the catalitic center. The purified enzyme has virtually no NOR activity. R. denitrificans also has aa3-type and cbb3-type cytochrome oxidases. Inhibition pattern by KCN of the purified NOR homologue and of the membrane fraction differed significantly, indicating that the contribution of NOR homologue to the total cytochrome oxidase activity is small. Results of Northern hybridization and SDS-PAGE showed that the abundance of both mRNA and the protein of NOR homologue increase in light or anaerobic conditions.
