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  • Title: Heme-linked proton dissociation of carbon monoxide complexes of myoglobin and peroxidase.
    Author: Hayashi Y, Yamada H, Yamazaki I.
    Journal: Biochim Biophys Acta; 1976 Apr 14; 427(2):608-16. PubMed ID: 5132.
    Abstract:
    It was found from spectrophotometric titration and proton balance measurement that the pKa value of a heme-linked protonation group of horseradish ferro-peroxidase C (donor:H2O2 oxidoreductase, EC 1.11.1.7) shifted from 7.25 to 8.25 upon combination with CO. The spectrophotometric titration experiment with myoglobin also revealed the presence of a heme-linked protonation group, the pKa value being 5.57 in myoglobin and 5.67 in the CO-myoglobin complex. It was concluded that the distinct shift of the pKa value in the case of peroxidase was attributable to the presence of a hydrogen bond between the sixth ligand and the distal base. The difference in the strength of such hydrogen bonding between peroxidase and myoglobin was discussed.
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