title: Low- and ultralow-temperature magnetic circular dichroism studies of reduced cytochromes P-450-LM2 and P-420-LM2 and of photo-products of their co-complexes. The spin-state and axial ligation of heme iron.
abstract: MCD spectra of reduced cytochromes P-450 and P-420 have been recorded in the spectral region 350-800 nm at temperatures 4.2-290 K and were compared with the respective low-temperature photolysed CO-complexes at 4.2 K. The MCD data are consistent with the suggestions that: the heme iron is high-spin in the reduced proteins and in the photolysed species; mercaptide is the protein-derived ligand of the heme iron in the reduced cytochrome P-450, as well as in its CO-complex; imidazole of histidine is the fifth ligand of the heme iron both in the reduced P-420 and its CO-complex; structural changes in the heme iron coordination sphere occur at CO-binding.
mesh_terms: D000818:Animals; D002248:Carbon Monoxide; D002942:Circular Dichroism; D003577:Cytochrome P-450 Enzyme System; D006418:Heme; D007527:Isoenzymes; D008862:Microsomes, Liver / Q000201:enzymology; D010777:Photochemistry; D010782:Photolysis; D011817:Rabbits
chemical_list: D007527:Isoenzymes; D006418:Heme; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System