Reactivity differences between haemoglobins. Part X. Spectral and reactivity studies on methaemoglobin Norfolk

Abstract

The spectrum of methaemoglobin Norfolk is widely different from that of human methaemoglobin A, and is shown to be consistent with the hypothesis that for a large proportion of the haems associated with the abnormal α-polypetide chains the imidazole ring of the distal histidine is bonded to the iron atom. The standard free energy and enthalpy of the reaction of fluoride ion with the haems associated with the normal β-polypeptide chains and the abnormal α-polypeptide chains are investigated and compared with the values for methaemoglobin A. Estimates are made of the standard free energy and entropy changes for the equilibrium between haems in the normal and abnormal configuration. The implications for other haemoproteins are discussed.