Urea carboxylase

Uracil (Ura, U) 199s, 203 tautomerism of 45 Urate oxidase 886 Urea 82s, 478s Urea carboxylase 730 Urease 478, 877,878... 

Urea carboxylase/ CO[NHal2 + 3HaO + HCOj ATP Biotin Avidin production... 

Urease (ATP-hydrolysing). Urea carboxylase (hydrolysing), ATP—urea amidolyase. Urea amido-lyase. 

Urea carbon dioxide ligase (urea carboxylase) (E.C. 6.3.4.6)... 

Other carboxylases are urea carboxylase and geranyl-CoA carboxylase. 

Biotin (referred to as vitamin H in humans) is an essential cofactor for a number of enzymes that have diverse metabolic functions. Almost a dozen different enzymes use biotin. Among the most well-known are acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, urea carboxylase, methylmalonyl-CoA decarboxylase, and oxaloacetate decarboxylase. Biotin serves as a covalent bound CO2 carrier for reactions in which CO 2 is fixed into an acceptor by carboxylases. Then this carboxyl group in an independent reaction can be transferred from the acceptor substrate to a new acceptor substrate by transcarboxylases, or the carboxyl group can be removed as CO 2 by decarboxylases. 

These convincing data showed that the I -N-ureido position of biotin serves as the site for carboxyl transfer with biotin enzymes. Lane also correctly pointed out that N O carboxyl migration might have preceded the participation of carboxybiotin in the enzymatic process. However, the well-established thermodynamic and kinetic stabilities of iV-acyl and JV-carboxy-2-imidazolidone derivatives render this possibility unlikely. Moreover, the urea carboxylase component of ATP-amidolyase, also a biotin-dependent enzyme, reversibly carboxylates urea to form iV-carboxyurea, a known example of carboxylation at the N-ureido position (333). 

P. A. Whitney and T. G. Cooper (1972), Urea carboxylase and allophanate hydroxylase. Two components of ATP Urea-lyase in S. cerevisiae. /. Biol Chem. 247, 1349-1353. 

An alternative mechanism of urea hydrolysis, also involving a two-step reaction sequence, has been demonstrated in yeast, algae and some fungi. Urea is first carboxylated to allophanate by urea carboxylase (urea CO2 ligase, EC 6.3.4.6), a reaction requiring ATP. Allophanate is then hydrolysed by allophanate hydrolase (allophanate amidohydrolase, EC 3.5.1.13) to CO2 and... 

Urea carboxylase and allophanate hydrolase. The Journal of Biological Chemistry, 2, 1349-1353. 

---