Magnetic circular dichroism studies of hepatic microsomal cytochrome P-450.
Magnetic circular dichroism (MCD) spectra have been measured for cytochrome P-450 (P-450) purified from phenobarbital-induced rabbit liver microsomes. The temperature dependence of some of the MCD spectra has also been determined. The MCD spectrum of oxidized P-450 seems to suggest that it is in a state intermediate between the ferric low-spin states. Model experiments suggest that this anomaly arises from the coordination of a thiolate anion to the heme. Reduced P-450 shows a very peculiar MCD spectrum; the spectrum as well as its temperature dependence suggest that the heme in reduced P-450 is a "mixture" in terms of redox and/or spin states. The MCD spectrum of the CO complex of reduced P-450 exhibits an apparent Faraday A term around 450 nm which consists of about 50% C term and 50% the other terms, indicating that it is not in a purely ferrous low-spin state. The CO complex of reduced cytochrome P-420 (P-420), on the other hand, shows an MCD spectrum characteristic of a ferrous low-spin heme. It is suggested from model experiments that the thiolate anion coordinates to the heme trans to CO in the P-450-CO complex. The Soret region of the MCD spectrum of the EtNC complex of reduced P-450 is characterized by two apparent A terms around 430 and 455 nm, whereas that of the corresponding complex of P-420 has only one apparent A term around 434 nm.
D000818:Animals; D002248:Carbon Monoxide; D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D003486:Cyanides; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification; D003580:Cytochromes; D005290:Ferric Compounds; D005296:Ferrous Compounds; D008280:Magnetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010084:Oxidation-Reduction; D011817:Rabbits
D003486:Cyanides; D003580:Cytochromes; D005290:Ferric Compounds; D005296:Ferrous Compounds; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System