INHIBITION OF COPPER QUINOPROTEIN AMINE OXIDASES FROM ASPERGILLUS-NIGER BY BENZOPHENANTHRIDINE ALKALOIDS/

Inhibition of copper/quinoprotein amine oxidases (EC 1.4.3.6), AO-I (d imer 2 X 75 kDa) and AO-II (monomer 80 kDa), from the fungus Aspergill us niger by benzophenanthridine alkaloids sanguinarine, chelerythrine, and fagaronine were studied. For both amine oxidases the alkaloids sh owed reversible noncompetitive inhibition of n-hexylamine oxidation wi th K-i 0.6, 0.9 and 2.8 mM for sanguinarine, chelerythrine, and fagaro nine, respectively. The values of the inhibition constants corresponde d to pK(R+) values for the iminium ion/pseudobase equilibrium of the a lkaloids. Since thio-compounds protected the enzymes against this inhi bition, the inhibition effect was ascribed to the interaction with a s ulfhydryl group essential for the enzymatic activity.