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Transition of hemoglobin between two tertiary conformations: Determination of equilibrium and thermodynamic parameters from the reaction of 5,5′-dithiobis(2-nitrobenzoate) with the CysF9[93]β sulfhydryl group

Okonjo, K. O. and Adediji, A. T. and Fodeke, A. A. and Adeboye, Omolara and Ezeh, C. V. (2007) Transition of hemoglobin between two tertiary conformations: Determination of equilibrium and thermodynamic parameters from the reaction of 5,5′-dithiobis(2-nitrobenzoate) with the CysF9[93]β sulfhydryl group. Biophysical Chemistry. pp. 56-62.

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Abstract

The equilibrium constant of the reaction of 5,5′-dithiobis(2-nitrobenzoate) with the CysF9[93]β sulfhydryl group of hemoglobin decreases by 2 to 3 orders of magnitude between pH 5.6 and 9. The reaction is coupled to the ionizations of two groups on the protein. At 25 °C one group has a pKa of 5.31±0.2 when hemoglobin is in its (tertiary) r conformation, typified by the thiolate anion form of CysF9[93]β; this changes to 7.73±0.4 in the (tertiary) t conformation, typified by the mixed disulfide form of the sulfhydryl. The second group ionizes with a pKa of 7.11±0.4 in the r conformation; this changes to 8.38±0.2 in the t conformation. Krt, the equilibrium constant for the r←→t isomerization process, is 0.22±0.06. The standard enthalpy and entropy changes for the isomerization are ΔHo rt=24.2 kJ mol−1 and ΔSo rt=68.8 JK−1mol−1, respectively.

Item Type: Article
Subjects: Q Science > QD Chemistry
Divisions: Faculty of Engineering, Science and Mathematics > School of Chemistry
Depositing User: Mr Adewole Adewumi
Date Deposited: 04 Jul 2011 18:50
Last Modified: 13 Dec 2011 21:13
URI: http://eprints.covenantuniversity.edu.ng/id/eprint/398

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