Distal His----Arg mutation in bovine myoglobin results in a ligand binding site similar to the abnormal beta site of hemoglobin Zurich (beta 63 His----Arg)

Carbon monoxide binding to a myoglobin mutant with distal arginine in place of histidine has been examined. The mutant is derived from a cDNA clone for Mb mRNA from fetal bovine skeletal muscle. The mutation only slightly perturbs visible/Soret spectra whereas the infrared spectrum of liganded CO is greatly modified to become nearly identical to Hb Zurich beta-subunit spectrum. The mutant IR spectra differ substantially from spectra of wild-type MbCO and normal HbCO beta-subunit. For both the Mb and the Hb the distal His----Arg mutation increases the affinity for CO and reduces the number of observed conformers. These results demonstrate that this mutation greatly reduces the differences between Mb and Hb in the structure and properties of its ligand binding sites.