ENTHALPY INVESTIGATION FOR ELUCIDATION OF THE TRANSITION CONCENTRATION FOR THE INTERACTION OF HORSERADISH-PEROXIDASE WITH SURFACTANTS

The interaction of horseradish peroxidase (HRP) with sodium n-dodecyl sulphate (SDS) as an anionic detergent and n-dodecyl trimethylammonium bromide (DTAB) as a cationic detergent was studied at pH 6.4 by micro calorimetry, equilibrium dialysis and spectroscopy. The enthalpy of un folding of the HRP by surfactants was determined from the calorimetric enthalpy and the enthalpy of binding was calculated from the Wyman an d van't Hoff relations. The transition concentration, [S](1/2), for th e denaturation of HRP by SDS and DTAB is enlightened from the enthalpi es of unfolding and of binding. Here, it has signified that the [S](1/ 2) point occurred at the end of HRP-surfactant electrostatic and the s tart of hydrophobic interactions. The unfolding of protein is mostly c ompleted at the end of electrostatic interactions. (C) 1997 Elsevier S cience B.V.