DYNAMICS OF SPIN-LABELED ALPHA-CHYMOTRYPSIN IN REVERSE MICELLES OF DIFFERENTLY CHARGED SURFACTANTS

Analysis and simulation of the EPR spectra of alpha-chymotrypsin spin- labelled at two sites (methionine-192 and serine-195) in water and sod ium bis(2-ethylhexyl) sulfosuccinate (AOT)-isooctane reverse micelles has provided information on the rate and nature of label motion in the se media. The correlation time of methionine-labelled chymotrypsin, an d the value of A(parallel to) for serine-labelled chymotrypsin in reve rse micelles have been studied as functions of surfactant charge [AOT, negative, and cetyltrimethylammonium bromide (CTAB), positive], of th e net protein charge above and below its isoelectric point, and of the addition of neutral co-surfactants. The results obtained are consiste nt with the 'water-shell' model oi protein solvation in these systems, with no evidence for any ionic significant interactions between prote in and surfactant headgroups.