title: 1H-NMR and EPR studies on met-azido and met-imidazole Dolabella auricularia myoglobin.
abstract: Met-azido and met-imidazole forms of the myoglobin from the mollusc Dolabella auricularia have been studied by 1H-NMR and EPR spectroscopy. In the mollusc myoglobin, in which His-E7 is replaced by Val, the guanidino group of Arg-E10 serves as an alternative hydrogen-bond donor to the bound ligand. Therefore, the guanidino group of Arg-E10 plays similar roles in ligand stabilization to that the His-E7 imidazole does in most vertebrate myoglobins. Differences in both the structural and electronic properties between Arg and His side chains largely affect the stability of met-azido and met-imidazole forms of the protein. Due to a weak stabilization by Arg-E10, the bound-N3- ligand is replaced by OH- at higher pH, although it is stable at neutral and acidic pH. In the absence of the hydrogen-bonding interaction, Fe-bound imidazole in met-imidazole Dolabella myoglobin is only stable at neutral pH and is removed at acidic pH and replaced by OH- at basic pH. The temperature study also revealed that the bound imidazole is replaced by OH- at higher temperature. These results confirm that the presence of steric hindrance between these bulky ligands and the long and bulky side chain of Arg-E10 in the distal pocket of the mollusc myoglobin. Thus steric effects contribute significantly to the stability of exogenous ligand in the distal pocket of myoglobin.
authors.affiliation: Department of Chemistry, University of Tsukuba, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: T
authors.initials: T
authors.lastname: Suzuki
authors.forename: H
authors.initials: H
authors.lastname: Hori
mesh_terms: D000818:Animals; D001386:Azides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008974:Mollusca / Q000737:chemistry*; D009211:Myoglobin / Q000737:chemistry*; D013696:Temperature
chemical_list: D001386:Azides; D007093:Imidazoles; D009211:Myoglobin; D006418:Heme