H93G myoglobin cavity mutant as versatile template for modeling heme proteins: magnetic circular dichroism studies of thiolate- and imidazole-ligated complexes.

Recent ligand binding and spectroscopic investigations of the myoglobin H93G cavity mutant are reviewed, revealing it to be a versatile template for the preparation of model heme complexes of defined structure. The H93G myoglobin cavity mutant is shown to be capable of forming mixed ligand adducts because of the difference in accessibility of the two sides of the ferric heme iron. With imidazole bound in the proximal cavity, H93G myoglobin also forms reasonably stable oxyferrous and oxoferryl derivatives, thereby providing a potential system to use for the study of such complexes with proximal ligands other than imidazole. In addition, thiolate-ligated ferric H93G derivatives are described that serve as spectroscopic models for the high-spin ferric state of cytochrome P450. All of the complexes described are characterized with magnetic circular dichroism spectroscopy, and they are compared to the appropriate derivatives of native myoglobin and P450.