Inhibition of monoamine oxidase modulates the behaviour of semicarbazide-sensitive amine oxidase (SSAO)

Summary.

The specific activity and kinetic behaviour of semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) towards benzylamine, in the rat heart, is affected by in vivo treatment with the non-selective monoamine oxidase (MAO) inhibitor tranylcypromine, but not by the selective MAO-A and -B inhibitors, clorgyline and lazabemide. SSAO activity was increased to 178% of control activity after 7 days of treatment with tranylcypromine. This increase appears to represent an increase in the limiting velocity (V_max) for benzylamine oxidation with no significant change in the K_m at that time-point. However, the K_m for benzylamine oxidation was found to decrease in both controls and treated groups, in a time-dependent manner, during the treatment regime. These findings suggest a link between SSAO and cellular stress and may have importance in the context of the recent finding that tissue-SSAO is identical to a vascular adhesion protein (VAP1), involved in the process of inflammation.