Competition between substrates for acetylcholinesterase and cholinesterase.

The kinetics of competition of pairs of two substrates for bovine erythrocyte acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) and horse serum cholinesterase (acylcholine acyl-hydrolase, EC 3.1.1.8) was studied so that the hydrolysis of only one substrate was measured at a time. The substrates were acetylthiocholine, were used as competiting substrates i.e. inhibitors. The substrate inhibition constants (Kss) and Michaelis constants for the reaction of a single substrate were also determined. It was concluded that the substrate inhibition site in the enzyme does not show up in the competition between two substrates.