Carbon Monoxide Binding to Pentacoordinate Mercaptide-heme Complexes: Kinetic Study on Models for Cytochrome P-450
Chang, C.K. and David Dolphin
Proc. Natl. Acad. Sci. U.S.A.
Mercaptide anions form exclusively penta-coordinate heme complexes [RS-heme] in polar and nonpolar solution over a wide range of mercaptide concentration. These complexes have a Soret peak at 408 nm and a formation constant of about 2.5 X 104 M-1 ), and combine with CO to give a CO-cytochrome P-450 type spectrum. Kinetics of CO binding to mercaptide-heme complexes [RS-heme] have been studied by the flash photolysis method. Characteristic constants for this reaction suggest close similarities between [CH3-(CH2)3 -S-heme] and cytochrome P-450. The reaction of alkoxide anion with heme has also been examined but no evidence was found for the existence of the [RO-heme-CO[ species.