title: Binding of CO to mutant alpha chains of hemoglobin M Iwate; evidence for distal imidazole ligation.
abstract: The optical contribution of the beta chains to the spectrum of hemoglobin M Iwate (alpha87his leads to tyr)2beta2a was subtracted with the aid of a computer so that the spectrum of ferric alpha chains was obtained. Tyrosinate binding to the heme is suggested from spectral resemblance to ferric heme phenolate in dimethyl sulfoxide. The slow reduction of the abnormal ferric alpha chains in hemoglobin M Iwate by dithionite was studied spectrophotometrically both in the presence and absence of CO. The rate of reduction was found to be dependent on the state of ligation of the normal beta chains. The CO-ligated form of the reduced alpha chains bears strong spectral resemblance to the CO-ligated form of the reduced beta chains suggesting similar structures for the heme-ligand complex. A model compound with similar optical properties to the CO-ligated protein can be prepared in dimethyl sulfoxide from hemin chloride, imidazole, and CO using chromous acetate as the heme reductant. Substitution of phenolate for imidazole produces a spectral entity so different from that observed in the protein as to rule out tyrosinate ligation to ferrous heme of the alpha chains when CO is bound.
mesh_terms: D002248:Carbon Monoxide / Q000378:metabolism*; D002263:Carboxyhemoglobin; D003201:Computers; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds; D006418:Heme; D006449:Hemoglobin M / Q000378:metabolism*; D006455:Hemoglobins, Abnormal / Q000378:metabolism*; D006801:Humans; D007093:Imidazoles; D010084:Oxidation-Reduction; D010636:Phenols; D013053:Spectrophotometry
chemical_list: D005290:Ferric Compounds; D006455:Hemoglobins, Abnormal; D007093:Imidazoles; D010636:Phenols; D006418:Heme; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; D006449:Hemoglobin M