Abstract: It was found that the autoxidation of various 6-N-substituted 5, 6-diaminouracils is strongly catalyzed by Cu (I1). Since this reaction is believed to be similar to one of the steps in the reaction catalyzed by the copper-containing amine oxidases, it has been studied in some detail. Evidence is presented that the catalyzed reaction involves the reduction of 02 to H202 and the oxidation of the diaminouracil by two electrons to 5, 6-diiminouracil or its ...