Interpretation of Mössbauer spectra of deoxyhaemoglobin taking into account the non-equivalence of the Fe²⁺ electronic structure in different subunits

Abstract

Human adult (HbA) and foetal (HbF) haemoglobins with different subunit structures (2α2β and 2α2γ subunits, respectively) in deoxy- and carbonmonoxyforms have been studied by Mössbauer spectroscopy at 87 K. The assumption that Mössbauer spectra of HbA and HbF should be interpreted taking into account the non-equivalence of the Fe²⁺ electronic structure in different subunits was made, and the Mössbauer spectra were approximated by superposition of two quadrupole split doublets with the requirement of equal areas. The differences of the quadrupole splittings related to α- and β-subunits in HbA and α- and β-subunits in HbF were in the range of 0·21–0·25 mm/s, and were in agreement with quantum chemical calculations for the Fe²⁺-porphyrin-imidazole complexes chosen as models of the active sites in α- and β-subunits of tetrameric HbA.