Volatile anesthetics-induced activation phenomena of α-chymotrypsin-catalyzed hydrolysis

Abstract

The rates of hydrolysis of p-nitrophenyl acetate (pNPA), p-nitrophenyl propionate (pNPP), p-nitrophenyl butanate (pNPB), and p-nitrophenyl valerate (pNPV) catalyzed by α-chymotripsin (α-CHT) were mesured with and without volatile anesthetics at 25.0°C. Halothane activated the hydrolysis of pNPA and pNPP, meanwhile inhibited that of pNPB and pNPV. The activation phenomena were explained by the existence of a 1:1 enzyme-anesthetics complex and the opening of an activated pathway. The rate constant of pNPA hydrolysis catalyzed by α-CHT of the activated pathway k A by halothane was 0.269 s −1, whereas that of the normal pathway was k 0 0.093 s −1. The free energy of activation was stabilized at 0.64 kcal/mol by halothane. The mechanisms of the activation and inhibition are discussed in terms of the molcular size of the substrate and anesthetics.