Biomaterial Database

Subunit interactions in aspartate transcarbamylase. Characterization of a complex between the catalytic and the regulatory subunits. 1975

J S Mort, and W W Chan

The complex formed when excess regulatory subunits (r2) of aspartate transcarbamylase is added to a dilute solution of the catalytic subunit (c3) has been further studied. By stabilizing the complex with saturating levels or r2, it was possible to perform ultracentrifugation in sucrose density gradients. The sedimentation coefficient of the complex (7.7 plus or minus 0.2 S) is intermediate between those of the catalytic subunit (5.8 S) and of the native enzyme (11.7 S). Consideration of the likely hydrodynamic properties of the complex suggests that this sedimentation coefficient may be consistent with the c3r6 structure previously proposed. The formation of c3r6 from c3 and r2 is readily reversible. At nonsaturating levels or r2, conversion to the native enzyme (c3r6) takes place. This conversion is inhibited by high concentrations of r2. The c3r6 complex shows Michaelis-Menten kinetics with a low Km for aspartate and considerable substrate inhibition. The pH activity profile at high aspartate concentrations is almost identical with that of the native enzyme. All of these observations suggest that c3r6 represents the relaxed (R) state of aspartate transcarbamylase. The insensitivity of c3r6 toward CTP or ATP can also be explained by considering c3r6 as a stabilized relaxed state. These properties of c3r6 have significant implications regarding the allosteric mechanism of the native enzyme.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D011485	Protein Binding	The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.	Plasma Protein Binding Capacity,Binding, Protein
D011487	Protein Conformation	The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).	Conformation, Protein,Conformations, Protein,Protein Conformations
D002627	Chemistry, Physical	The study of CHEMICAL PHENOMENA and processes in terms of the underlying PHYSICAL PHENOMENA and processes.	Physical Chemistry,Chemistries, Physical,Physical Chemistries
D003597	Cytosine Nucleotides	A group of pyrimidine NUCLEOTIDES which contain CYTOSINE.	Cytidine Phosphates,Nucleotides, Cytosine,Phosphates, Cytidine
D004926	Escherichia coli	A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.	Alkalescens-Dispar Group,Bacillus coli,Bacterium coli,Bacterium coli commune,Diffusely Adherent Escherichia coli,E coli,EAggEC,Enteroaggregative Escherichia coli,Enterococcus coli,Diffusely Adherent E. coli,Enteroaggregative E. coli,Enteroinvasive E. coli,Enteroinvasive Escherichia coli
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D000255	Adenosine Triphosphate	An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter.	ATP,Adenosine Triphosphate, Calcium Salt,Adenosine Triphosphate, Chromium Salt,Adenosine Triphosphate, Magnesium Salt,Adenosine Triphosphate, Manganese Salt,Adenylpyrophosphate,CaATP,CrATP,Manganese Adenosine Triphosphate,MgATP,MnATP,ATP-MgCl2,Adenosine Triphosphate, Chromium Ammonium Salt,Adenosine Triphosphate, Magnesium Chloride,Atriphos,Chromium Adenosine Triphosphate,Cr(H2O)4 ATP,Magnesium Adenosine Triphosphate,Striadyne,ATP MgCl2
D000494	Allosteric Regulation	The modification of the reactivity of ENZYMES by the binding of effectors to sites (ALLOSTERIC SITES) on the enzymes other than the substrate BINDING SITES.	Regulation, Allosteric,Allosteric Regulations,Regulations, Allosteric
D001221	Aspartate Carbamoyltransferase	An enzyme that catalyzes the conversion of carbamoyl phosphate and L-aspartate to yield orthophosphate and N-carbamoyl-L-aspartate. (From Enzyme Nomenclature, 1992) EC 2.1.3.2.	Aspartate Transcarbamylase,Co(II)-Aspartate Transcarbamoylase,Ni(II)-Aspartate Transcarbamoylase,Carbamoyltransferase, Aspartate,Transcarbamylase, Aspartate