NMR studies of hemoproteins. VI. Acid-base transitions of ferric myoglobin and its imidazole complex.
220 MHz proton NMR was applied to the acid-base transition of ferric myoglobin and its imidazole complex. In horse and sperm whale ferric myoglobins: (1) pH-dependent shift of heme-ring methyl signals above p2H 10 was analyzed on the basis of rapid exchange between alkaline and acidic forms by the use of pK value 9.1 of acid-base transition in 1H20 solution; (2) limiting shifts of three methyl signals were reasonably determined for purely alkaline form. For the imidazole complex: (3) a drastic high field shift of each signal was observed above p2H 9.0, whereas N0methyl imidazole complex did not exhibit such a shift, which suggests the 2H+ dissociation from liganded imidazole greater than N2H. It is concluded thns.
D000818:Animals; D001665:Binding Sites; D003903:Deuterium; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles; D007501:Iron / Q000032:analysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D009211:Myoglobin; D011485:Protein Binding; D011487:Protein Conformation; D013053:Spectrophotometry; D014907:Whales
D007093:Imidazoles; D009211:Myoglobin; D003903:Deuterium; D007501:Iron