Kinetics of the alkaline tetramer → dimer dissociation in liganded human hemoglobin: A laser light-scattering stopped-flow study

D. P. Flamig, L. J. Parkhurst

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Abstract

The first-order dissociation of tetrameric HbCO to the dimer has been studied over the pH range 10.30-11.57 in a light-scattering stopped-flow apparatus using argon-ion laser excitation. The first-order dissociation rate constant varies from 0.25 sec-1 to 24.0 sec-1 over this pH interval. A semilogarithmic plot of k versus pH has a slope of 2.56 at pH 11.07, the midpoint. The pH dependence of the dissociation of the tetramer is consistent with progressive titration of α12 and β12 salt bridges. At pH 10.66 the dissociation rates of HbO2, HbCO, methemoglobin, and HbCN vary less than 20% from their mean value. A study of the dissociation kinetics as a function of protein concentration allows one to obtain both association and dissociation rate constants, and hence equilibrium constants, for the tetramer ⇆ dimer reaction. In this manner, equilibrium constants were obtained on protein solutions with less than 15 sec of exposure to dissociating conditions.

Original languageEnglish (US)
Pages (from-to)3814-3816
Number of pages3
JournalProceedings of the National Academy of Sciences of the United States of America
Volume74
Issue number9
DOIs
StatePublished - Jan 1 1977

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