Domain structures of urea amidolyase and related proteins. Proteins that share the amidase (allophanate hydrolase) or the biotin-carboxylation domain are listed. The domains colored in grey are those that are not shared among these proteins. The domain structures are based on the InterPro protein domain database . The abbreviations and approximate amino-acid lengths are given with the protein names. Amidase and urea carboxylase sequences exist as domains within the urea amidolyase protein or as single proteins by themselves. Similarly, the biotin-carboxylation sequence exists as a domain in various proteins as well as by itself as in the biotin-carboxylase protein.