Alteration of human myoglobin proximal histidine to cysteine or tyrosine by site-directed mutagenesis: characterization and their catalytic activities.

Two mutant proteins of human myoglobin (Mb) that exhibit altered axial ligations were prepared by site-directed mutagenesis of a cloned gene for human Mb. The normal axial ligand residue, histidine 93(F8), was replaced with cysteine or tyrosine, resulting in H93C or H93Y Mb, respectively. Cysteine or tyrosine coordination to the ferric heme iron is verified by electronic absorption, 1H-NMR, EPR spectra, and redox potentials of Fe2+/Fe3+ couple. Their mono-oxygenation activities of styrene are also discussed.