Diamine oxidases are enzymes that destroy toxic biogenic amines. Diamine oxidase, DAD, is an enzyme protein complex that catalyzes the inactivation of toxic biologically active amines - produced by the body with the participation of enzymes of the enzymatic systems “transamination” and “decarboxylation”, linked together into a single system of exchange of biogenic amines in the body. Classification of diamino acids Early studies showed that this group of compounds can occur either individually or together with groups of functional groups. Four different types of diamines and nine isomers of their corresponding metabolites have been identified. Research may show both positive and negative effects of diamines on mammals. A separate group of studied compounds includes the formation of histidine rings, which are beta-metone rings.