Oxygen Binding to Mercaptide-Heme Complexes. Models for Reduced Cytochrome P-450
Chang, C.K. and David Dolphin
J. Am. Chem. Soc.
Mercaptide-heme complexes with n-butyl mercaptide ion as the axial ligand were capable of reversible oxygen binding at -45 oC in aqueous dimethylacetamide. The Soret band of the mercaptide-heme-O2 complex was split into 2 peaks at 476 nm and 378 nm. This type of 2-Soret-peak spectra was a general feature of all CO- and O2-ferrous porphyrin complexes ligated with mercaptide. The notable spectral discrepancies between the mercaptide-heme complex and the oxygenated cytochrome P 450 enzyme system suggested that while in the ferric deoxy and ferrous CO forms of cytochrome P 450 a mercaptide may serve as the axial ligand, the oxygenated form of cytochrome P 450 cannot be bound to a mercaptide.