Characterization of Flavocytochrome c552 from the Thermophilic Photosynthetic Bacterium Chromatium tepidum

A Mr 68 kDa flavocytochrome c552 has been isolated from the thermophilic photosynthetic purple sulfur bacterium Chromatium tepidum and shown to consist of a Mr 25 kDa subunit that contains two covalently bound heme c and a Mr 43 kDa subunit that probably contains a single FAD. The prosthetic group content, absorbance spectra, and subunit composition of the C. tepidum flavocytochrome are quite similar to those previously reported for the flavocytochrome c552 isolated from a mesophilic Chromatium species, Chromatium vinosum. The oxidation-reduction properties of the hemes present in the C. tepidum flavocytochrome have been characterized by titrations, the effect of temperature on the catalytic activity of the protein has been investigated, and the heme environment has been characterized using resonance Raman spectroscopy.