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Rate of quaternary structure change in hemoglobin measured by modulated excitation
Journal article   Open access

Rate of quaternary structure change in hemoglobin measured by modulated excitation

F A Ferrone and J J Hopfield
Proceedings of the National Academy of Sciences - PNAS, v 73(12), pp 4497-4501
01 Dec 1976
DOI: https://doi.org/10.1073/pnas.73.12.4497
PMID: 1070000
url
https://doi.org/10.1073/pnas.73.12.4497View
Published, Version of Record (VoR)Open Access (License Unspecified),  Open

Abstract

Using a novel technique of modulated photo-dissociation of carbon monoxide from hemoglobin, we have obtained the rates for conversion between the two quaternary states, R, and T, at 3-fold ligation. Our measurements at pH 7 and 22 degrees give rates of 780 +/- 40 sec-1 for going from R to T, and 2500 +/- 200 sec-1 from T to R. This yields an equilibrium constant of 0.31 +/- 0.04, which is in good agreement with previous estimates. The degree of agreement between this equilibrium constant and that predicted from the allosteric model provides a new, quantitative test of the allosteric description. A sequential model for the change in structure was found incompatible with the data, even if kinetic subunit inequivalence was assumed. The technique described here is quite general and can be used as long as the system under investigation can be repetitively excited in a regime in which it responds linearly to the excitation.

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