The copper amine oxidases are ubiquitous enzymes that occur in bacteria, yeast, plants, and mammals. These enzymes catalyze the two-electron oxidative deamination of a primary amine to produce the corresponding aldehyde and ammonia, with subsequent two-electron reduction of dioxygen to hydrogen peroxide. To carry out this reaction, copper amine oxidases, which belong to the new class of proteins designated quinoproteins, contain two ...