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Enthalpy Change of Allosteric Transition in Human Haemoglobin A
Author(s) -
Amire Olasoji A.,
Masoudy J.,
Saboury A. A.,
MoosaviMovahedi A. A.,
Ogunmola G. B.
Publication year - 2004
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.200400032
Subject(s) - chemistry , tetramer , allosteric regulation , enthalpy , deoxygenation , salt bridge , molecule , hydrogen bond , thermodynamics , oxygen , gibbs free energy , crystallography , organic chemistry , biochemistry , enzyme , physics , gene , mutant , catalysis
Oxygen equilibria of haemoglobin were analysed according to a binding isotherm proposed by Amire ( Bull. Chem. Soc. Jpn. 1994, 67, 7 ) 1 to obtain the intrinsic oxygen association constants to the molecule. Two sets of binding sites in haemoglobin were identified, which were ascribed to R 2 and T forms of the molecule. The average intrinsic association constants determined as a function of temperature gave a heat of oxygenation of‐76 ± 4 kJ mol −;1 (tetramer). A microcalorimetrically determined heat of deoxygenation of oxyhaemoglobin by dithionite gave −267 ± 10 kJ mol −1 (tetramer). From these results, the heat of allostery of −234 ± 24 kJ mol −1 for haemoglobin tetramer was obtained, yielding allosteric energy per salt bridge of‐29 ± 3 kJ. This result suggests that salt‐bridge may, in fact, be thermochemically equivalent to hydrogen bonds.