Studies on cobalt myoglobins and hemoglobins. The effect of the removal of the α-141 arginine residue on the functional and electronic properties of iron-cobalt hybrid hemoglobins

Des-arg iron-cobalt hybrid hemoglobins, des-arg α(Co)₂β(Fe)₂, and des-arg α(Fe)₂β(Co)₂, in which the α-141 arginine residues are digested by carboxypeptidase B, were prepared, and their functional and EPR spectral properties were examined. The overall oxygen affinities of the α and β subunits in both iron and cobalt hemoglobin tetramers were increased by the removal of this arginine residue and that of the α subunits was markedly influenced as compared with the β subunits. In des-arg hemoglobins, the difference in the oxygen affinities between the α and β subunits was smaller than that in the unmodified hemoglobins. The rate of carbon monoxide binding to the ferrous subunits in deoxy iron-cobalt hybrid hemoglobins were incresed by 6- and 10-fold for the α(Fe)₂ and β(Fe)₂ subunits, respectively, by this modification. The deoxy EPR spectrum of des-arg α(Co)₂β(Fe)₂ showed that the stripped deoxy des-arg hemoglobins are predominantly in the oxy quaternary structure. Comparison of the functional and EPR spectral data of des-arg hemoglobins with those of the unmodified hemoglobins indicated that the ligand affinity of the β subunits is higher than that of the α subunits in the low affinity, quaternary structure of deoxyhemoglobin, but that this difference is small in the oxy, high affinity, quaternary structure.