Urea carboxylase (UC) catalyses a two-step, ATP- and biotin-dependent carboxylation reaction of urea. It is composed of biotin carboxylase (BC), carboxyltransferase (CT), and biotin carboxyl carrier protein (BCCP) domains. The CT domain of UC consists of four subdomains, named A, B, C and D. This domain covers the C and D subdomains of the CT domain. This domain covers the whole length of kipI (kinase A inhibitor) from Bacillus subtilis [1]. It can also be found in S. cerevisiae urea amidolyase Dur1,2, which is a multifunctional biotin-dependent enzyme with domains for urea carboxylase and allophanate (urea carboxylate) hydrolase activity[2].

1: A novel histidine kinase inhibitor regulating development in Bacillus subtilis. Wang L, Grau R, Perego M, Hoch JA; Genes Dev. 1997;11:2569-2579. PMID:9334321

2: Dur3 is the major urea transporter in Candida albicans and is co-regulated with the urea amidolyase Dur1,2. Navarathna DH, Das A, Morschhauser J, Nickerson KW, Roberts DD; Microbiology. 2011;157:270-279. PMID:20884691