alpha-chymotrypsin superactivity in cetyltrialkylammonium bromide-rich media

alpha-Chymotrypsin (alpha-CT) activity was tested with N-glutaryl-L-phenyla lanine p-nitroanilide in buffered media with added cationic surfactants. Th e effect of the commercial cetyltrimethylammonium bromide (CTABr) was compa red with that of three other surfactants with ethyl (CTEABr), propyl (CTPAB r), and butyl (CTBABr) head groups. These were synthesized and purified in this laboratory. Surfactant head groups provided distinct environments that largely modulated the catalytic performance. Larger alkyl head group hydro phobicity led to a marked enhancement of alpha-CT activity. CTBABr-rich med ia induced the highest superactivity. Kinetic measurements were performed in Tris-HCl buffer at a surfactant conc entration either below or above CMC, and alpha-CT superactivity occurred in both media. Positive interactions between the enzyme and surfactants happe ned independently of the supramolecular organization of the medium. The rea ction followed the Michaelis-Menten kinetics. The substrate to micelle aggr egates binding constant was used to calculate the substrate concentration a vailable for catalysis. The k(cat) to K-m ratio was in CTBABr-rich media al ways higher than in pure buffer and depended on the surfactant concentratio n, alpha-CT superactivity depended on the pH value of buffer solution. Enzy me inactivation followed a single-step mechanism in pure buffer and a serie s mechanism in the presence of a surfactant. The rate of activity decay obe yed a first-order kinetics.