The dissociation of carbon monoxide from the alpha and the beta subunits of human carbonmonoxy hemoglobin.
We have measured the intrinsic CO dissociation rates from the subunits of the human hemoglobin tetramers (alpha CO beta NO)2 and (alpha NO beta CO)2 using microperoxidase and a stopped-flow spectrophotometer. The dissociation of NO is negligible. The rate constants for the and the subunits are similar (0.014 s-1 vs. 0.011 s-1, respectively, at pH 7, 20 C; and 0.016 s-1 for both in the presence of inositol hexaphosphate), indicating that they are equivalent in the first step of the CO dissociation. Therefore, the chain unequality observed in the third and fourth steps (Samaja, M., Rovida, E., Niggeler, M., Perrella, M., and Rossi-Bernardi, L. (1987). J. Biol. Chem.: 262, 4528-4533) are not due to the intrinsic properties of the subunits, but to the conformational state of the molecule.
Dipartimento di Scienze e Tecnologie Biomediche, Universita' di Milano, Italy.
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Samaja
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Rovida
D000494:Allosteric Regulation; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates; D007700:Kinetics; D046911:Macromolecular Substances; D009609:Nitrous Oxide
D007295:Inositol Phosphates; D046911:Macromolecular Substances; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; D009609:Nitrous Oxide