Isolation and characterization of two soluble heme c-containing proteins from Chromatium vinosum

The photosynthetic purple sulfur bacterium Chromatium vinosum has been shown to possess two previously undetected heme c-containing, soluble proteins. One is an acidic, c-type cytochrome with a molecular weight of 12 300 and an oxidation-reduction midpoint potential (at pH 8.0) of ?82 mV. The other protein is a basic protein with a molecular weight of 11 900 and an oxidation-reduction midpoint potential (at pH 8.0) of ?110 mV. The basic protein, in both oxidized and reduced forms, has optical spectra similar to those of myoglobin and the oxidized C. vinosum protein exhibits a high-spin heme EPR spectrum similar to that of metmyoglobin. Furthermore, the basic C. vinosum protein binds CO and O₂. The spectra of the CO and O₂ complexes show significant similarities with the respective myoglobin complexes. Possible functions for an O₂-binding protein in C. vinosum are discussed.