Augustinsson_1950_Acta.Chem.Scand_4_536

The kinetics of the inhibition of the acetylcholine-esterase by methylene blue has been studied using cow erythrocytes as enzyme source. Methylene blue is a true competitive inhibitor and behaves in a similar way found previously for other quaternary ammonium bases. The optimum acetylcholine concentration, characteristic of this esterase, is changed to higher concentration in the presence of the dye. The higher inhibitor concentration the higher is the optimum acetylcholine concentration. Great differences in degree of inhibition are obtained when the action of the dye on the acetylcholine-esterase is compared with that on the serum cholinesterase. Evaluating the inhibition as function of methylene blue concentration the dissociation constant (KI ) of the inhibitor-enzyme complex was found to be 5.7 X 10-7. A higher value of KI is obtained when the enzyme solution has been incubated with the inhibitor before mixed with the substrate.