title: Reduction of methemerythrin by deoxymyoglobin: a protein-protein redox reaction not involving electron-transfer proteins.
abstract: The stoichiometry and kinetics of reaction of methemerythrin with the deoxy forms of myoglobin and hemoglobin have been examined at I = 0.2 M and 25 degrees C. One mole of methemerythrin (on the basis of the monomer unit containing two irons) reacts with 2 mol of deoxymyoglobin and with 0.5 mol of deoxyhemoglobin. All reactions are second order. Rate constants for reaction with deoxymyoglobin are 0.25 M-1s-1 (Phascolopsis gouldii) and 5.6 M-1s-1 (Themiste pyroides) at pH 6.3. There is little effect of raising the ionic strength to 1.35 M and only a small decrease in rate when the pH is adjusted to 8.2. The rate constant for reaction of deoxyhemoglobin with P. gouldii methemerythrin is approximately 0.1 M-1s-1 at pH 6.3. Metmyohemerythrin from T. pyroides reacts slightly slower than the octamer form (k = 2.0 M-1s-1 at pH 6.3 and 7.0). Oxymyoglobin is converted to metmyoglobin by methemerythrin. The electron-transfer path is discussed and a self-exchange rate constant for hemerythrin assessed as 10(-3) M-1s-1 on the basis of Marcus's theory.
mesh_terms: D000818:Animals; D000845:Annelida; D004579:Electron Transport; D006422:Hemerythrin / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008667:Metalloproteins / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism*; D009994:Osmolar Concentration; D010084:Oxidation-Reduction
chemical_list: D006422:Hemerythrin; D006454:Hemoglobins; D046911:Macromolecular Substances; D008667:Metalloproteins; D009211:Myoglobin; C019004:methemerythrin