Spectroscopic and kinetic properties of an oxygen-binding heme protein from Chromatium vinosum

Resonance Raman and electron paramagnetic resonance spectroscopy have been utilized to identify histidine as an axial heme ligand in a high spin, heme c-containing protein isolated from the photosynthetic purple sulfur bacterium Chromatium vinosum. Resonance Raman spectroscopy has also been used to characterize the CO adduct of the C. vinosum hemoprotein. Resonance Raman spectra of the heme site obtained within 10 ns of CO photolysis from the ferrous hemoprotein are virtually identical to those of the unligated protein, indicating that there is little or no rearrangement of the heme pocket in response to ligand photolysis. The equilibrium constant for CO binding to the ferrous hemeprotein was measured to be 1.7 X 10(-5) M-1 and the CO association rate constant determined to be 5.4 X 10(3) M-1 S-1. The quantum efficiency for photodissociation of the hemoprotein X CO complex was greater than or equal to 0.9.