The Single Superoxide Dismutase of Rhodobacter capsulatus Is a Cambialistic, Manganese-Containing Enzyme

ABSTRACT

The phototrophic bacterium Rhodobacter capsulatus contains a single, oxygen-responsive superoxide dismutase (SOD_Rc) homologous to iron-containing superoxide dismutase enzymes. Recombinant SOD_Rc, however, displayed higher activity after refolding with Mn²⁺, especially when the pH of the assay mixture was raised. SOD_Rc isolated from Rhodobacter cells also preferentially contains manganese, but metal discrimination depends on the culture conditions, with iron fractions increasing from 7% in aerobic cultures up to 40% in photosynthetic cultures. Therefore, SOD_Rc behaves as a Mn-containing dismutase with cambialistic properties.