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Effect of anionic surfactant on the reaction of 2,2(1)-dithiobispyridine with bovine oxyhemoglobin as a function of
C O Aboluwoye1, K O Okonjo, A A Moosavi-Movahedi
1Department of Chemistry, Ondo State University, Ado-Ekiti, Nigeria.
Abstract:
The reaction of bovine oxyhemoglobin with 2,2(1)-dithiobispyridine in the absence and presence of sodium n-dodecyl sulphate has been studied as a function of pH and temperature. The quantitative analysis of the pH dependence of the apparent second order rate constants shows that two ionizable groups are linked to the reaction in the native form. These are His HC3 (146) beta and Cys F9 (93) beta. Their pKa values are 6.5 and 8.5. In the denatured form, only one ionizable group is the modulating factor. This group is Cys F9 (93) beta. Its pKa is 8.35. The activation parameters for the reaction of the denatured form of bovine oxyhemoglobin with 2,2(1)-dithiobispyridine are lower than those of the native form. The reason is that the sulphydryl group is more exposed in the denatured form that in the native form. In addition, there is an increase in the rupturing of salt bridges and hydrogen bonds between the CO and NH peptide backbone. There is also a decrease in van der Waals interactions in the denatured form compared to the native form.