Structural and catalytic properties of enzymes in reverse micelles

Abstract

Structural and catalytic properties of two enzymes—α-chymotrypsin and horse liver alcohol dehydrogenase (LADH)—are studied in bis(2-ethylhexyl) sodium sulfosuccinate (AOT)-isooctane reversemicelle solutions. Circular dichroism (CD) and electron paramagnetic resonance spectroscopy (EPR) studies show little change in α-chymotrypsin structure upon incorporation into reverse micelles. For LADH, large perturbations in structure are seen upon solubilization in reverse micelles. These structural properties explain, in part, the observed activity of these two enzymes in reverse micelles. α-Chymotrypsin retains activity in reverse micelles and, in some cases, displays enhanced activity. A sixfold increase in the turnover number was observed in w 0 = 10 reverse micelles. LADH has low activity in reverse micelles compared to that in aqueous solution. At w 0 = 70, the turnover number of LADH is 18% of the aqueous value. Active-site titrations show a decrease in active enzyme concentration for both enzymes upon incorporation into reverse micelles. Little change in the structure of both LADH and α-chymotrypsin is observed with change of water content in the reverse-micelle system.