The location of tryptophan, N-acetyltryptophan and alpha-chymotrypsin in reverse micelles of AOT: a fluorescence study.

The spectroscopic properties of alpha-chymotrypsin (alpha-Chym), L-tryptophan (Trp) and N-acetyl-L-tryptophan (NAT) solubilized in hydrated reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate in iso-octane were followed by fluorescence as a function of the amount of intramicellar water and initial pH. The lack of pH dependence observed for Trp in these systems, as opposed to what occurs in bulk water, and the similarities found for the protein in both media foresee different locations of these probes. In reverse micelles, fluorescence quenching studies using acrylamide emphasize the existence of structural alterations within the protein when its global charge changes from positive (pH = 7) to negative (pH = 10). The ensemble of the data points to an interfacial location of the zwitterionic Trp, an intermediate region of less tightly bound water for the location of the anionic Trp and NAT and an almost bulk water environment for alpha-Chym.