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Spectral evidence for 3 metal linked ionization equilibria in the interaction of cobalt ii horse liver alcohol dehydrogenase ec 1.1.1.1 with coenzyme and substrate


Journal of Inorganic Biochemistry 17(3): 227-236
Spectral evidence for 3 metal linked ionization equilibria in the interaction of cobalt ii horse liver alcohol dehydrogenase ec 1.1.1.1 with coenzyme and substrate
The visible absorption bands in the region 525-575 nm of the catalytic Co ion in Co(II) horse liver alcohol dehydrogenase show characteristic pH-dependent changes in the free enzyme and its complexes with NAD+ and NAD+ plus ethanol or 2,2,2-trifluoroethanol. In the free enzyme, the change of the coordination environment has an apparent pK of .apprx. 9.4. In the binary complex with NAD+ the spectral changes are complex, indicating changes in the coordination sphere in a lower pH range with an estimated pK value of .apprx. 7.9. The ternary complexes enzyme.cntdot.NAD+.cntdot.ethanol and enzyme.cntdot.NAD+.cntdot.2,2,2-trifluoroethanol exhibit very similar, characteristic spectral features; their apparent pK values are 6.3 and < 4, respectively. These pK values are ascribed to the ionization of the alcohol bound in the ternary complexes. The catalytic Co senses changes in the ionization state of the protein when going from low pH forms to high pH forms in the absence and presence of coenzyme and substrate/inhibitor.


Accession: 006459674



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