Equilibrium Reaction Of Human Methemoglobin A

Abstract

A study has been carried out on the sulfhydryl group reactivities of human methemoglobin A and its azide complex with 2,2\'-dithiobispyridine (2-DTP) in the presence and absence of inositol hexaphosphate (IHP) in order to evaluate electrostatic effects on reactivity and the relationship between conformational states and reactivity. The reaction was monitored spectrophotometrically by the formation of 2-thiopyridone (the product of the reaction) with an absorption peak at 343 nm at 20 °C.
The binding of IHP to methemoglobin A (met-HbA) diminishes the reactivity of β-93 sulfhydryl group towards 2DTP. This effect was used to determine the pH profile of the binding constants of IHP to the surface of the protein while changing the complex at the heme iron. Work was also done on the equilibrium reaction of azide ion with IHP- and 2DTP- chemically modified met-Hb A as a function of pH, and an equilibrium relationship was developed for reactions both at the heme iron and at the surface of the methemoglobin molecule. The result shows that binding at the heme by ligands such as azide ion affects the orientation of charge groups on the surface of the met-Hb molecule as well as binding of organic phosphate.


IFE Journal of Science Vol. 9 (2) 2007 pp. 225-230