PROSITE documentation PDOC00091
Aspartate and ornithine carbamoyltransferases signature


Aspartate carbamoyltransferase (EC (ATCase) catalyzes the conversion of aspartate and carbamoyl phosphate to carbamoylaspartate, the second step in the de novo biosynthesis of pyrimidine nucleotides [1]. In prokaryotes ATCase consists of two subunits: a catalytic chain (gene pyrB) and a regulatory chain (gene pyrI), while in eukaryotes it is a domain in a multi-functional enzyme (called URA2 in yeast, rudimentary in Drosophila, and CAD in mammals [2]) that also catalyzes other steps of the biosynthesis of pyrimidines.

Ornithine carbamoyltransferase (EC (OTCase) catalyzes the conversion of ornithine and carbamoyl phosphate to citrulline. In mammals this enzyme participates in the urea cycle [3] and is located in the mitochondrial matrix. In prokaryotes and eukaryotic microorganisms it is involved in the biosynthesis of arginine. In some bacterial species it is also involved in the degradation of arginine [4] (the arginine deaminase pathway).

It has been shown [5] that these two enzymes are evolutionary related. The predicted secondary structure of both enzymes are similar and there are some regions of sequence similarities. One of these regions includes three residues which have been shown, by crystallographic studies [6], to be implicated in binding the phosphoryl group of carbamoyl phosphate. We have selected this region as a signature for these enzymes.


The residue in position 3 of the pattern allows to distinguish between an ATCase (Glu) and an OTCase (Lys).

Last update:

October 1993 / Text revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

CARBAMOYLTRANSFERASE, PS00097; Aspartate and ornithine carbamoyltransferases signature  (PATTERN)


1AuthorsLerner C.G. Switzer R.L.
TitleCloning and structure of the Bacillus subtilis aspartate transcarbamylase gene (pyrB).
SourceJ. Biol. Chem. 261:11156-11165(1986).
PubMed ID3015959

2AuthorsDavidson J.N. Chen K.C. Jamison R.S. Musmanno L.A. Kern C.B.
TitleThe evolutionary history of the first three enzymes in pyrimidine biosynthesis.
SourceBioEssays 15:157-164(1993).
PubMed ID8098212

3AuthorsTakiguchi M. Matsubasa T. Amaya Y. Mori M.
TitleEvolutionary aspects of urea cycle enzyme genes.
SourceBioEssays 10:163-166(1989).
PubMed ID2662961

4AuthorsBaur H. Stalon V. Falmagne P. Luethi E. Haas D.
TitlePrimary and quaternary structure of the catabolic ornithine carbamoyltransferase from Pseudomonas aeruginosa. Extensive sequence homology with the anabolic ornithine carbamoyltransferases of Escherichia coli.
SourceEur. J. Biochem. 166:111-117(1987).
PubMed ID3109911

5AuthorsHoughton J.E. Bencini D.A. O'Donovan G.A. Wild J.R.
TitleProtein differentiation: a comparison of aspartate transcarbamoylase and ornithine transcarbamoylase from Escherichia coli K-12.
SourceProc. Natl. Acad. Sci. U.S.A. 81:4864-4868(1984).
PubMed ID6379651

6AuthorsKe H.-M. Honzatko R.B. Lipscomb W.N.
TitleStructure of unligated aspartate carbamoyltransferase of Escherichia coli at 2.6-A resolution.
SourceProc. Natl. Acad. Sci. U.S.A. 81:4037-4040(1984).
PubMed ID6377306

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