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

Des-arg iron-cobalt hybrid hemoglobins, des-arg alpha(Co)2 beta (Fe)2, and des-arg alpha (Fe)2 beta (Co)2, in which the alpha-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 alpha and beta subunits in both iron and cobalt hemoglobin tetramers were increased by the removal of this arginine residue and that of the alpha subunits was markedly influenced as compared with the beta subunits. In des-arg hemoglobins, the difference in the oxygen affinities between the alpha and beta 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 increased by 6- and 10-fold for the alpha (Fe)2 and beta (Fe)2 subunits, respectively, by this modification. The deoxy EPR spectrum of des-arg alpha (Co)2 beta (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 beta subunits is higher than that of the alpha subunits in the low affinity, quaternary structure of deoxyhemoglobin, but that this difference is small in the oxy, high affinity, quaternary structure.