This domain is the second or third structural domain in copper amine oxidases, it is known as the N3 domain. Its function is uncertain. The catalytic domain can be found in Pfam:PF01179. Copper amine oxidases are a ubiquitous and novel group of quinoenzymes that catalyse the oxidative deamination of primary amines to the corresponding aldehydes, with concomitant reduction of molecular oxygen to hydrogen peroxide. The enzymes are dimers of identical 70-90 kDa subunits, each of which contains a single copper ion and a covalently bound cofactor formed by the post-translational modification of a tyrosine side chain to 2,4,5-trihydroxyphenylalanine quinone (TPQ).

1: Crystal structure of a quinoenzyme: copper amine oxidase of Escherichia coli at 2 A resolution. Parsons MR, Convery MA, Wilmot CM, Yadav KD, Blakeley V, Corner AS, Phillips SE, McPherson MJ, Knowles PF; Structure 1995;3:1171-1184. PMID:8591028