Abstract
-3 is complex. The removal of the terminal HisHC3(146)� of haemoglobin A by enzymatic cleavage with carboxypeptidase A breaks the salt bridge between HisHC3(146)� and AspFG1(94)� and reduces the strain on CysF9(93)� sulphydryl group. The pH dependence profiles of the second order rate constant for the reaction of DTNB with CysF9(93)� sulphydryl group of the modified haemoglobin A derivatives at 50 mmol dm -3 became simple with significant reduction in the reaction rates contrary to expectations. The implication is that CysF9(93)� becomes occluded and hence less reactive. The mean pKas of the ionizable groups linked to the reactivity of CysF9(93)� sulphydryl group of des-HisHC3(146)� human haemoglobin A were 5.52 ± 0.01 and 8.29 ± 0.1. These values are assigned to HisH21(143)� and CysF9(93)� amino acid residues, respectively.
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