Biomaterial Database

Kinetics and reaction mechanism of the carbamylphosphate synthetase of a multienzyme aggregate from yeast. 1975

D M Aitken, and P F Lue, and J G Kaplan

We have studied the kinetics and reaction mechanism of the carbamylphosphate synthetase of an enzyme aggregate functioning in the pyrimidine pathway of yeast. MG--ATP was found to be one of the substrates of the enzyme reaction which was activated by free Mg-2+ and inhibited by free ATP. Feedback inhibition by UTP was non-competitive with respect to both glutamine and bicarbonate. Potassium ions were essential for activity and could not be replaced by sodium. Glutamine could be replaced partially by ammonium ions as nitrogen donor. A bicarbonate-dependent cleavage of ATP was shown to take place in the absence of L-glutamine; L-glutamate was a competitive inhibitor of L-glutamine and the enzyme was shown to synthesize ATP when incubated with ADP and carbamyl phosphate. The reaction mechanism was found to involve sequential addition of the substrates bicarbonate and Mg--ATP and release of ADP, followed by addition of the third substrate glutamine. The purine nucleotide XMP had a pronounced activating effect on the enzyme, acting at a site different from that of UTP. Saturating levels of Mg--ATP eliminated this activation.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008274	Magnesium	A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.
D008956	Models, Chemical	Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.	Chemical Models,Chemical Model,Model, Chemical
D009097	Multienzyme Complexes	Systems of enzymes which function sequentially by catalyzing consecutive reactions linked by common metabolic intermediates. They may involve simply a transfer of water molecules or hydrogen atoms and may be associated with large supramolecular structures such as MITOCHONDRIA or RIBOSOMES.	Complexes, Multienzyme
D010770	Phosphotransferases	A rather large group of enzymes comprising not only those transferring phosphate but also diphosphate, nucleotidyl residues, and others. These have also been subdivided according to the acceptor group. (From Enzyme Nomenclature, 1992) EC 2.7.	Kinases,Phosphotransferase,Phosphotransferases, ATP,Transphosphorylase,Transphosphorylases,Kinase,ATP Phosphotransferases
D011188	Potassium	An element in the alkali group of metals with an atomic symbol K, atomic number 19, and atomic weight 39.10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the WATER-ELECTROLYTE BALANCE.
D002221	Carbamyl Phosphate	The monoanhydride of carbamic acid with PHOSPHORIC ACID. It is an important intermediate metabolite and is synthesized enzymatically by CARBAMYL-PHOSPHATE SYNTHASE (AMMONIA) and CARBAMOYL-PHOSPHATE SYNTHASE (GLUTAMINE-HYDROLYZING).	Carbamoyl Phosphate,Dilithium Carbamyl Phosphate,Carbamyl Phosphate, Dilithium,Phosphate, Carbamoyl,Phosphate, Carbamyl,Phosphate, Dilithium Carbamyl
D002223	Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)	An enzyme that catalyzes the formation of carbamoyl phosphate from ATP, carbon dioxide, and glutamine. This enzyme is important in the de novo biosynthesis of pyrimidines. EC 6.3.5.5.	Carbamyl Phosphate Synthase (Glutamine),Carbamoyl-Phosphate Synthase (Glutamine),Carbamoylphosphate Synthetase II,Carbamyl Phosphate Synthase II,Carbamyl-Phosphate Synthase (Glutamine),Synthetase II, Carbamoylphosphate
D004305	Dose-Response Relationship, Drug	The relationship between the dose of an administered drug and the response of the organism to the drug.	Dose Response Relationship, Drug,Dose-Response Relationships, Drug,Drug Dose-Response Relationship,Drug Dose-Response Relationships,Relationship, Drug Dose-Response,Relationships, Drug Dose-Response
D004789	Enzyme Activation	Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme.	Activation, Enzyme,Activations, Enzyme,Enzyme Activations