Cholinesterase: substrate inhibition and substrate activation

The relationship between activities and substrate concentrations (pS-curves ) was analysed for reactions of acetylcholinesterase (EC 3.1.1.7) and butyr ylcholinesterase (EC 3.1.1.8). Catalytic constants K-m, K-ss, V-m, n and b were calculated fi-om the Michaelis, Haldane, Hill and Webb equations in or der to assess whether a given substrate also acts as an inhibitor or activa tor. It is suggested that the term substrate inhibition should only be attr ibuted to substrates revealing bell-shaped pS-curves, while the terms appar ent substrate inhibition or apparent substrate activation should relate to calculated values of the catalytic constants.