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Tertiary Conformational Transition In Horse Haemoglobin Induced By Inositol Hexakisphosphate

Omotosho, O. E. and Okonjo, K. O. and Omotosho, T. V. and Rotimi, Solomon and Chinedu, S. N. (2013) Tertiary Conformational Transition In Horse Haemoglobin Induced By Inositol Hexakisphosphate. The FASEB Journal, 27 (1).

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The red blood cell of the domestic horse contains two haemoglobin types. The two haemoglobins were separated on a column of carboxymethylcellulose. The equilibrium constant, Kequ, for the reaction of 5,5'-dithiobis(2-nitrobenzoate) — DTNB — with the CysF9[93]β sulfhydryl group of each haemoglobin was determined at 25°C as a function of pH. The reactivity of CysF9[93]β is affected by allosteric effectors such as the proton (H+) and inositol hexakisphosphate (inositol-P6). Between pH 5.6 and 9.0 Kequ decreased by about two to four orders of magnitude, demonstrating that H+ is a heterotropic allosteric effector of haemoglobin with respect to its reaction with DTNB. Inositol-P6 also decreased Kequ by about two to four orders of magnitude across the experimental pH range. CysF9[93]β exists in two tertiary conformations, r and t, in dynamic equilibrium. Krt, the equilibrium constant for the r t conformational transition, was determined for each of the two horse haemoglobins from an analysis of the pH dependence of Kequ. The calculations from the pH dependence of Kequ showed that the pKa values of the ionisable groups coupled to the DTNB reaction vary between 5.0 and 8.9. The equilibrium constants, Krt, for the r t tertiary structure transition, were 0.143 ± 0.05 and 0.446 ± 0.22 for the fast and slow stripped horse haemoglobins respectively. In the presence of inositol-P6, Krt for the fast and slow were 2.219 ± 0.79 and 2.214 ± 0.83 respectively. The results show that inositol-P6 increases the relative population of the t tertiary conformation. So, it increases the affinity of CysF9[93]β by changing the relative distribution of two protein conformations.

Item Type: Article
Subjects: Q Science > QC Physics
Q Science > QD Chemistry
Q Science > QH Natural history > QH301 Biology
Divisions: Faculty of Medicine, Health and Life Sciences > School of Biological Sciences
Depositing User: Mrs Patricia Nwokealisi
Date Deposited: 26 Nov 2015 13:43
Last Modified: 26 Nov 2015 13:43

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