Effect of pH on the activity of eel esterase towards different substrates

Abstract

The dependence upon pH of the hydrolysis of acetylthiocholine, phenyl acetate, p-nitrophenyl acetate and p-methoxyphenyl acetate by true cholinesterase from the electric eel was measured. The pH-activity curves of these substrates above pH 7 become largely independent of pH, whatever the length of the incubation period. These results confirm the existence of the 2d component in the esteratic site, postulated earlier, namely the electrophilic group G2, and indicate that the latter functions via hydrogen-bonding with the oxygen atom attached to the alkyl radical of the ester group. The implications of these findings for the mechanism of enzymic hydrolysis are discussed.