Flavocytochromes c(552) from chromatium vinosum and chromatium tepidum

The purpose of this work is to study electron transfer reactions in photosynthetic bacteria. Flavocytochrome C552 from the purple sulfur bacterium Chromatium vinosum is an unusual heme protein which contains two hemes and one flavin per molecule. This protein catalyzes the oxidation of sulfide to sulfur using a soluble c -type cytochrome as an electron acceptor. The characteristics of flavocytochrome C552 and its complex with equine cytochrome cwere investigated by proton NMR spectroscopy. The study indicated that the two hemes are non-equivalent magnetically. The downfield region of the NMR spectra presented a non-symmetrical pattern. One of the hemes is like cytochrome c and the other one is more sensitive to medium effects such as, pH or ionic strength. Near-IR MCD spectra provided unambiguous evidence for two non-equivalent hemes, both with histidinemethionine axial ligation in the presence of 50% ethylene glycol. Analysis of EPR spectra suggested heterogeneity in the axial ligation of one of the two hemes at neutral pH. It was concluded that this heme occurs as a mixture of forms with histidine-lysine and histidine-methionine axial ligation.