REDUCTION OF METHEMERYTHRIN BY DEOXYMYOGLOBIN - PROTEIN-PROTEIN REDOX REACTION NOT INVOLVING ELECTRON-TRANSFER PROTEINS

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 °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-1 s-1 (Phascolopsis gouldii) and 5.6 M-1 s-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 ~0.1 M-1 s-1 at pH 6.3. Metmyohemerythrin from T. pyroides reacts slightly slower than the octamer form (k=2.0 M-1 s-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-1 on the basis of Marcus's theory. © 1979, American Chemical Society. All rights reserved.