Tertiary conformational transition in sheep hemoglobins induced by reaction with 5,5´-dithiobis(2-nitrobenzoate) and by binding of inositol hexakisphosphate

Okonjo, Kehinde O.; Adeogun, Idowu Abideen; Babalola, Jonathan O.

doi:10.1016/j.bpc.2009.10.006

Cited by 3 publications

(1 citation statement)

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“…Furthermore, Ho and co-workers have concluded that mutations or chemical modifications at the F9(93)β site affect the salt bridge and the organic phosphatebinding site and also destabilize the T quaternary state [8]. By studying the reactivity of CysF9(93)β as a function of pH it is demonstrated that inositol hexakisphosphate (inositol-P 6 ), an organic phosphate, raises the pK a of HisHC3(146)β of human haemoglobins A and S by one pK a unit, thereby strengthening the HisHC3/AspFG1 salt bridge and reducing the reactivity of the sulphydryl group [9]. These interesting findings raise the possibility that sulphydryl groups located at other positions in the haemoglobin molecule might provide equally interesting information.…”

Section: Introductionmentioning

confidence: 99%

High ionic strength or presence of inositol hexakisphosphate reverses the unusually low pKA of CYSH3(125)Β of guinea pig haemoglobin

Babalola¹

2012

Bull. Chem. Soc. Eth.

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ABSTRACT. The kinetics of the reaction of 5,5'-dithiobis(2-nitrobenzoate) with guinea pig oxy-and carbonmonoxyhaemoglobin are biphasic. The two phases differ in rate by two orders of magnitude. For the fast phase, quantitative analysis of the pH dependence of the apparent second order rate constant, kapp, shows that it has all the characteristics associated with the reaction of CysF9 (93)β, a sulphydryl group that is invariant in all mammalian haemoglobins. The slow kinetic phase is assigned to CysH3(125)β. Quantitative analysis of the pH dependence of kapp for this phase at 50 mM ionic strength gave an unusually low pKa of 6.0 for this sulphydryl group. Published data on guinea pig haemoglobin show that it has a much-enhanced acid Bohr effect compared to human haemoglobin. This indicates that CysH3(125)β functions as an acid Bohr group in guinea pig haemoglobin. Comparison with human haemoglobin indicates that this cysteine reduces the alkaline Bohr effect of guinea pig haemoglobin between pH 7 and 6, and enhances its acid Bohr effect below pH 6. From kinetic data collected at high salt concentration, and in the presence of inositol hexakisphosphate, it is shown that the pKa of the sulphydryl increases to ca 9 and 7.7, respectively. Under these conditions, CysH3(125)β ceases to be an acid Bohr group.

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Section: Introductionmentioning

confidence: 99%