The effect of debrisoquin on MAO A and MAO B activities

To examine the mode of action of debrisoquin (DEB), we studied the effect of this drug in vitro on MAO A and MAO B enzyme activities. DEB was shown to be a competitive inhibitor of highly purified human MAO A and MAO B enzyme activities. DEB inhibited placental MAO A with a Ki value of 0.5 μM and liver MAO B with a Ki value of 8.8 μM, 18-fold greater effect on the A form. Kynuramine was used as substrate for both enzymes. Additional studies using a dilution technique showed that DEB was a reversible inhibitor of both forms of the enzyme. The results of this study show that DEB is a potent competitive and reversible inhibitor of both MAO A and MAO B enzymes.