title: Magnetic-circular-dichroism studies of haem a and its derivatives.
abstract: The low-temperature m.c.d.(magnetic-circular-dichroism) spectra of haem a derivatives are presented. It is shown that reduced haem a in pyridine contains the low-spin ferrous ion and that oxidized haem a in the presence of excess imidazole has the low-spin ferric form. Both the m.c.d. and the absorption spectra of haem a in excess pyridine are changed by the addition of excess sodium dithionite into a form similar to that of haems b and c. This is interpreted in terms of an attack, by reduced pyridine, at the 8-formyl group of the haem a ring. This leads to a partial assignment of the electronic spectrum of haem a.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D004227:Dithionite; D006418:Heme / Q000031:analogs & derivatives; D010084:Oxidation-Reduction; D011725:Pyridines; D013054:Spectrophotometry, Atomic
chemical_list: D011725:Pyridines; D004227:Dithionite; D006418:Heme