Effects of Head Group of Cationic Surfactants on the Hydrolysis of p-Nitrophenyl Acetate Catalyzed by α-Chymotrypsin

The kinetics of hydrolysis of p-nitrophenyl acetate catalyzed by alpha-chymotrypsin (alpha-CT) has been studied in the presence of several cationic surfactants having different head groups maintaining the dodecyl hydrophobic residue and bromide counterion. The enzyme activity was tested in the presence of dodecyl trimethylammonium bromide (DTAB), dode-cylpyridinium bromide (DPB), dodecyldimethylethanolammonium bromide (DDMEAB), dodecyldiethylethanolammonium bromide (DDEEAB), benzyldimethyldodecylammonium bromide (BDDAB), and dodecyltriphenylphosphonium bromide (DTPB) surfactants. The extent of superactivity depends upon head groups of surfactants. The activity of alpha-CT depends on the surfactant concentration and it varies with the surfactant head group dimensions (DTPB > DDEEAB > DTAB > BDDAB > DDMEAB > DPB). For all surfactants, DTPB exhibits highest superactivity. The effects of surfactants on the apparent kinetic parameters like Michaelis constant K-m and the catalytic constant k(cat) have been determined. (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 377-381, 2009