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Aspartate CarbamoyltransferaseOrnithine CarbamoyltransferaseDihydroorotaseCarbamyl PhosphateCarbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)Cytidine TriphosphatePhosphonoacetic AcidMoritellaDihydroorotate OxidaseAspartic AcidAllosteric RegulationEscherichia coliX-Ray DiffractionCarboxyl and Carbamoyl TransferasesOrnithine Carbamoyltransferase Deficiency DiseaseProtein ConformationOrnithineAspartate AminotransferasesCitrullinePhosphotransferases (Carboxyl Group Acceptor)Orotic AcidKineticsOrnithine-Oxo-Acid TransaminaseAmino Acid SequenceCarbamoyl-Phosphate Synthase (Ammonia)HydrolasesArgininosuccinate LyaseArginineMolecular Sequence DataArginaseEnzyme StabilitySodium BenzoateArsenatesTransferasesTransaminasesPyrococcus furiosusArgininosuccinate Synthase

EscherichiaCarbamoyl phosphateTranscarbamylaseCatalyticAllosteric regulationEnzyme-substraPyrimidine synthesisCatalyzesShifting the enzymeReactionStateComplexModelAllosteric

Escherichia2

• The aim of the project was to characterize intrachain and interchain interactions involved in the regulatory behaviour of a model allosteric enzyme of known 3-dimensional structure: aspartate carbamoyltransferase (ATCase) of Escherichia coli, a protein consisting of distinct catalytic and regulatory subunits. (europa.eu)
• Early studies found that Escherichia coli ATCase is regulated by the level of CTP, a nucleotide with a pyrimidine ring. (rcsb.org)

Carbamoyl phosphate2

• The synthesis of pyrimidines starts one step earlier than ATCase, when the enzyme carbamoyl-phosphate synthase (CPSase) creates carbamoyl phosphate from several common cellular building blocks. (rcsb.org)
• Two enzymes in glutamine-dependent carbamoyl-phosphate synthase (GLNase and CPSase) together create carbamoyl phosphate, ATCase connects it to aspartate, and dihydroorotase (DHOase) closes it into a ring that will be become the pyrimidine base (PDB entries 5dou , 4c6i , 5g1n ). (rcsb.org)

Transcarbamylase3

• Aspartate transcarbamylase, with catalytic subunits in red, regulatory subunits in blue, and CTP in green. (rcsb.org)
• This has been termed "feedback inhibition," and study of the enzyme aspartate transcarbamylase helped reveal how it's done. (rcsb.org)
• Aspartate transcarbamylase (ATCase) performs an early step in the production of pyrimidine rings, which are used to build nucleotides in DNA and RNA. (rcsb.org)

Catalytic3

• The results obtained show that the R1-C4 interaction is essential for the establishment of the enzyme conformation having low affinity for aspartate (T state), and consequently for the existence of cooperactivity between the catalytic sites. (europa.eu)
• The structure revealed that ATCase is a large complex, with six catalytic chains arranged in the center, surrounded by three pairs of regulatory chains. (rcsb.org)
• Notice that the human ATCase portion includes only catalytic subunits, without the regulatory subunits found in the bacterial enzyme complex. (rcsb.org)

Allosteric regulation2

• More recently, the E. coli enzyme aspartate carbamoyltransferase (ATCase) has become another good example of allosteric regulation. (wikipedia.org)
• Exploring how ATCase flows between states (tense, relaxed and enzyme-substrate complex) over time based on modifiers and substrate can assist in grasping the concept of allosteric regulation. (wolfram.com)

Enzyme-substra1

• Plot of how ATCase switches between its states of tense, relaxed and enzyme-substrate complex. (wolfram.com)

Pyrimidine synthesis3

• This model studies a naturally occurring allosteric reaction: the first step in the pyrimidine synthesis, catalyzed by the allosteric enzyme aspartate carbamoyltransferase (ATCase). (wolfram.com)
• Some bacteria only make one form of CPSase, so it's not the best enzyme to regulate, so pyrimidine synthesis is regulated by the second enzyme in the pathway, ATCase, which is only used to build pyrimidines. (rcsb.org)
• Many variations on ATCase and the other enzymes of pyrimidine synthesis have been observed in different organisms. (rcsb.org)

Catalyzes2

• ATCase catalyzes the carbamoylation of aspartate by carbamoylphosphate (CP). (europa.eu)
• ATCase catalyzes the first step in the pyrimidine synthesization process and is affected by adenosine triphosphate (ATP), uridine triphosphate (UTP) and cytidine triphosphate (CTP). (wolfram.com)

Shifting the enzyme1

• Activity of the ATCase is regulated by shifting the enzyme from a tense, low-affinity state to a relaxed, high-affinity state. (wolfram.com)

Reaction1

• CTP is also one of the final products of the synthesis reaction chain, and if CTP or UTP is too low compared to ATP, then the activity of ATCase is increased to compensate. (wolfram.com)

State1

• Initially, ATCase is almost exclusively in a complex state, but as aspartate runs out, it switches back into its relaxed and tense states. (wolfram.com)

Complex1

• For instance, take a look at PDB entry 3d6n for an example of a complex that includes both ATCase and DHOase. (rcsb.org)

Model2

• ATCase can be seen in the left part of the model in its two states, relaxed (ATCase_R) and tense (ATCase_T). (wolfram.com)
• Plot of how carbamoyl aspartate and aspartate change over time as the model simulates. (wolfram.com)

Allosteric2

• More recently, the E. coli enzyme aspartate carbamoyltransferase (ATCase) has become another good example of allosteric regulation. (wikipedia.org)
• Reconstituted holoenzyme comprising two CPC trimers and three wild-type regulatory (R) dimers was shown by enzyme assays to be devoid of the homotropic and heterotropic allosteric properties characteristic of wild-type ATCase. (nih.gov)