Dynamics of spin-labelled α-chymotrypsin in reverse micelles of differently charged surfactants

Abstract

Analysis and simulation of the EPR spectra of α-chymotrypsin spin-labelled at two sites (methionine-192 and serine-195) in water and sodium bis(2-ethylhexyl) sulfosuccinate (AOT)–isooctane reverse micelles has provided information on the rate and nature of label motion in these media. The correlation time of methionine-labelled chymotrypsin, and the value of A_∥ for serine-labelled chymotrypsin in reverse micelles have been studied as functions of surfactant charge [AOT, negative, and cetyltrimethylammonium bromide (CTAB), positive], of the net protein charge above and below its isoelectric point, and of the addition of neutral co-surfactants. The results obtained are consistent with the ‘water-shell’ model of protein solvation in these systems, with no evidence for any ionic significant interactions between protein and surfactant headgroups.