Inactivation of beef plasma amine oxidase by sulfide

Sulfide irreversibly inactivates beef plasma amine oxidase in a time-dependent reaction. Mercaptoacetic acid and 2-mercaptoethanol do not inactivate the enzyme. The sulfide complex displayed an intense absorption band at 360 nm (epsilon = 6000 M-1 cm-1, per mol of copper) that is assigned as sigma S leads to Cu(II) ligand to metal charge-transfer transition. However, this band slowly decreased in intensity; the final spectrum resembles the spectrum of the dithionite-reduced enzyme. Bleaching at approximately 450-500 nm specifically indicates that the organic cofactor is reduced. EPR parameters for the sulfide complex differ significantly from those observed for the native amine oxidase. Superhyperfine structure, attributable to coordinated nitrogens, is clearly evident. Time-dependent reduction of Cu(II) that parallels the kinetics and absorbance changes was also observed by EPR. The amine oxidaseazide complex was inactivated by sulfide at a considerably slower rate than the resting enzyme. Since azide is known to coordinate to Cu(II) in beef plasma amine oxidase, the data strongly suggest that enzyme-bound copper is the site of action for inhibition by sulfide.