Aspartate carbamoyltransferase

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carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase
Identifiers
Symbol	CAD
Entrez	790
HUGO	1424
OMIM	114010
RefSeq	NM_004341
UniProt	P27708
Other data
EC number	2.1.3.2
Locus	Chr. 2 p22-p21

Aspartate carbamoyltransferase (also know as ATCase or aspartate transcarbamoylase) catalyzes the first step in the pyrimidine biosynthetic pathway (EC 2.1.3.2).

The enzyme is a multi-subunit protein complex composed of 12 subunits (300 kDa in total). The stoichiometry of the subunits is C₆R₆; forming 2 trimers of catalytic subunits (34 kDa) and 3 dimers of regulatory subunits (17 kDa). The overall structure is roughly triangular in shape. The particular arrangement of catalytic and regulatory subunits in this enzyme afford the complex with strongly allosteric behaviour with respect to its substrates. This protein is an archetypal example of allosteric modulation of fine control of metabolic enzyme reactions. It therefore does not follow Michaelis-Menten kinetics, but lies between the R and T states.

The binding of substrate to the catalytic subunits result in an equilibrium shift towards the R state, whereas binding of CTP to the regulatory subunits results in an equilibrium shift towards the T state. Binding of ATP to the regulatory subunits results in an equilibrium shift towards the R state.

External links

• MeSH Aspartate+carbamoyltransferase

v • d • e Metabolism: amino acid metabolism - nucleotide enzymes
Purine metabolism	Anabolism R5P->IMP: Ribose-phosphate diphosphokinase - Amidophosphoribosyltransferase - Phosphoribosylglycinamide formyltransferase - AIR synthetase (FGAM cyclase) - Phosphoribosylaminoimidazole carboxylase - Phosphoribosylaminoimidazolesuccinocarboxamide synthase - IMP synthase IMP->AMP: Adenylosuccinate synthase - Adenylosuccinate lyase - reverse (AMP deaminase) IMP->GMP: IMP dehydrogenase - GMP synthase - reverse (GMP reductase) Nucleotide salvage Hypoxanthine-guanine phosphoribosyltransferase - Adenine phosphoribosyltransferase Catabolism Adenosine deaminase - Purine nucleoside phosphorylase - Guanine deaminase - Xanthine oxidase - Urate oxidase
Pyrimidine metabolism	Anabolism CAD (Carbamoyl phosphate synthase II, Aspartate carbamoyltransferase, Dihydroorotase) Dihydroorotate dehydrogenase - Orotidine 5'-phosphate decarboxylase/Uridine monophosphate synthetase CTP synthase Catabolism Dihydropyrimidine dehydrogenase - Dihydropyrimidinase/DPYS - Beta-ureidopropionase/UPB1
Deoxyribonucleotides	Ribonucleotide reductase - Nucleoside-diphosphate kinase - DCMP deaminase - Thymidylate synthase - Dihydrofolate reductase
see also disorders, intermediates

v • d • e Enzymes: multienzyme complexes

CAD (Carbamoyl phosphate synthase II, Aspartate carbamoyltransferase, Dihydroorotase) - Cholesterol side-chain cleavage enzyme - Cytochrome b6f complex - Electron transport chain - Fatty acid synthetase complex - Glycine decarboxylase complex - Mitochondrial trifunctional protein (HADHA, HADHB) - Oxoglutarate dehydrogenase - Phosphoenolpyruvate sugar phosphotransferase system - Photosynthetic reaction center complex proteins - Photosystem - Polyketide synthase - Pyruvate dehydrogenase complex (E1, E2, E3) - Sucrase-isomaltase complex -Tryptophan synthase