Aspartate carbamoyltransferase

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

Aspartate carbamoyltransferase
Escherichia coli aspartate carbamoyltransferase heterododecamer with catalytic subunits coloured red and blue, and regulatory subunits in orange. PDB: 4FYY​
Identifiers
EC no.2.1.3.2
CAS no.9012-49-1
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO
Search
PMCarticles
PubMedarticles
NCBIproteins
Human carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, dihydroorotase
Identifiers
SymbolCAD
NCBI gene790
HGNC1424
OMIM114010
RefSeqNM_004341
UniProtP27708
Other data
EC number2.1.3.2
LocusChr. 2 p22-p21
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StructuresSwiss-model
DomainsInterPro

In E. coli, the enzyme is a multi-subunit protein complex composed of 12 subunits (300 kDa in total). The composition of the subunits is C6R6, forming 2 trimers of catalytic subunits (34 kDa) and 3 dimers of regulatory subunits (17 kDa). The particular arrangement of catalytic and regulatory subunits in this enzyme affords the complex with strongly allosteric behaviour with respect to its substrates. The enzyme is an archetypal example of allosteric modulation of fine control of metabolic enzyme reactions.

ATCase does not follow Michaelis–Menten kinetics. Instead, it lies between its low-activity, low-affinity "tense" and its high-activity, high-affinity "relaxed" states. The binding of substrate to the catalytic subunits results 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.

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