Parameters of the interaction of sodium dodecyl sulfate with human hemoglobin

It was shown that sodium dodecyl sulfate at concentrations not exceeding th e critical micelle concentrations (0-1.9 mM) induced the conversion of oxy- and methemoglobin but not deoxyhemoglobin to hemichrome. The concentration dependences of hemichrome formation were represented as Hill plots, and th e parameters of detergent binding were estimated. OxyHb in 20 mM potassium - phosphate buffer, pH 6.8, has two groups of binding sites: the first grou p is characterized by the Hill constant n(1) = 2 and the concentration of h alfsaturation [SDS](50) = 0.8 mM, and the second group is characterized by the Hill constant n(2) = 8 and [SDS](50) = 0.9 mM. In the case of metHb one group of binding sites with the Hill constant n = 2 and halfsaturation con centration [SDS](50) = 0.2 mM was observed. An increase in environmental pH to 7.9 decreased the affinity of Hb for SDS. It is suggested that primary binding sites for SDS in oxyHb coincide with the anion-binding center of th e Hb molecule. The interaction of the detergent with these binding sites in duced a structural transition of the hemoprotein molecule. As a result of t his transition, secondary binding sites were exposed. In a model system (he min - imidazole in ethanol solution), the enthalpy of the transition of hem in from a high-spin to a low-spin state was estimated to be 47 +/- 7 kJ/mol .