title: Evidence for cooperative hydrogen ligand binding to sperm whale metmyoglobin.
abstract: Potentiometric titrations of sperm whale metmyoglobin from pH 10 to 3 shows the well-known exposure of groups between pH 4.5 and 4. However the reverse titration, at low protein concentration, results in the regeneration of its ionic property in the form of a reversible hysteresis, which was obtained by titrating the same solution twice. The Soret intensity band indicates reversibility for about 94%. Apomyoglobin shows an acid-base reversible titration from pH 9.5 to 3. Since the analysis by electrostatic interaction models do not adequately describe the overall ionic equilibria of metmyoglobin, a cooperative model was introduced. The model exactly reproduces the titration curve, indicating that 6 groups ionize with a cooperative coefficient of 9. The cooperative model explains the anomalous behaviour toward hydrogen ions and the incomplete spectral reversibility of sperm whale metmyoglobin as a molecular mechanism with physiological significance.
authors.affiliation: Dipartimento di Medicina Sperimentale, Facoltà di Medicina, Università La Sapienza, Rome.
authors.forename: L
authors.initials: L
authors.lastname: Forlani
authors.forename: C
authors.initials: C
authors.lastname: Ioppolo
authors.forename: W J
authors.initials: WJ
authors.lastname: Evans
authors.forename: M A
authors.initials: MA
authors.lastname: Marini
mesh_terms: D000818:Animals; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008786:Metmyoglobin / Q000737:chemistry / Q000378:metabolism*; D008962:Models, Theoretical; D010100:Oxygen; D011487:Protein Conformation; D014907:Whales / Q000378:metabolism*
chemical_list: D008024:Ligands; D008786:Metmyoglobin; D010100:Oxygen