Proximal ligand control of heme iron coordination structure and reactivity with hydrogen peroxide: investigations of the myoglobin cavity mutant H93G with unnatural oxygen donor proximal ligands.

摘要: Abstract The role of the proximal heme iron ligand in activation hydrogen peroxide and control spin state coordination number proteins is not yet well understood. Although there are several examples amino acid sidechains with oxygen atoms which can act as potential ligands, occurrence protein-derived donor ligation natural protein systems quite rare. sperm whale myoglobin cavity mutant H93G Mb (D. Barrick, Biochemistry 33 (1994) 6546) has its histidine replaced by glycine, a mutation leaves an open capable accommodation variety unnatural ligands. This provides convenient system for studying ligand–protein interactions. Molecular modeling active site indicates that sufficient size to accommodate benzoate phenolate conformations allow their come within binding distance iron. In addition, may occupy orientation allows one carboxylate atom ligate while other bonding serine 92. ferric complexes have been prepared characterized UV-visible MCD spectroscopies. adduct shows characteristics six-coordinate high-spin complex. To our knowledge, this first known example complex anionic ligand. displaced at alkaline pH upon reaction peroxide. five-coordinate whose spectra distinct from those 93 tyrosine (H93Y Mb) myoglobin. stable exhibits reduced reactivity relative both native myoglobin, exogenous ligand-free derivative Mb. These observations indicate identity important influence on