Center for Bioinformatics
Oxidoreductases | Transferases | Hydrolases | Lyases | Isomerases | Ligases

Basic Information

Enzyme Number

6.3.5.5

Official Name

carbamoyl-phosphate synthase (glutamine-hydrolysing)

Name from literature

carbamoyl phosphate synthase

Pathway from literature

the de novo UTP biosynthetic pathway

Pathway from KEGG

Amino Acid Metabolism; Glutamate metabolism; map00251

Nucleotide Metabolism; Pyrimidine metabolism; map00240

Organisms

Rat (10116)

Comments

The product carbamoyl phosphate is an intermediate in the biosynthesis of arginine and the pyrimidine nucleotides [4]. The enzyme from Escherichia coli has three separate active sites, which are connected by a molecular tunnel that is almost 100 A in length [8]. The amidotransferase domain within the small subunit of the enzyme hydrolyses glutamine to ammonia via a thioester intermediate. The ammonia migrates through the interior of the protein, where it reacts with carboxy phosphate to produce the carbamate intermediate. The carboxy-phosphate intermediate is formed by the phosphorylation of bicarbonate by ATP at a site contained within the N-terminal half of the large subunit. The carbamate intermediate is transported through the interior of the protein to a second site within the C-terminal half of the large subunit, where it is phosphorylated by another ATP to yield the final product, carbamoyl phosphate [6].

Rate-limiting Description

"Assuming that plasma NH3 levels reflect those in mitochondria, the NH3 concentration yielding half-maximal rates of urea synthesis (close to 2 microM) was in the same range as Km for the rate-limiting step in ureagenesis, carbamoyl phosphate synthetase (EC 6.3.4.16)." (3812736)

"The data indicate that the expression of urea cycle enzymes, in particular that of carbamoyl phosphate synthetase which is the rate-limiting step, is up-regulated by partial hepatectomy." (7608487)

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  Last Modified: 2009-03-24  
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