Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.3.5.5 (CPS)
 1,262 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Acetylglutamate and ATP accelerate the oxidative inactivation of carbamoyl phosphate synthetase I by mixtures of Fe3+, ascorbate, and O2, but the mechanism of the inactivation differs with each ligand. In the presence of acetylglutamate, MgATP prevents, Mg2+, Mn2+, and catalase have no effect, and EDTA increases the inactivation, and the two phosphorylation steps of the enzyme reaction are lost simultaneously. The inactivation appears to be mediated by dehydroascorbate and is associated with the reversible oxidation of the highly reactive cysteines 1327 and 1337 and with oxidation of non-thiolic groups in the second 40-kDa domain (the enzyme consists of 4 domains of 40, 40, 60, and 20 kDa, from the amino terminus). The data are consistent with oxidation of groups at or near the site for ATPA (ATPA yields Pi; ATPB yields carbamoyl phosphate), and with the location of this site at the interphase between the second 40-kDa and the COOH-terminal domains. The oxidative inactivation promoted by ATP is inhibited by Mg2+, Mn2+, catalase, and EDTA, is not mediated by dehydroascorbate, and is not associated with oxidation of cysteines 1327 and 1337. Groups in the 60-kDa domain are oxidized. The phosphorylation step involving ATPB is lost preferentially, and the inactivation and the binding of ATPB exhibit the same dependency on the concentration of ATP. The results indicate that the oxidation is catalyzed by FeATP bound at the site for ATPB and support the binding of ATPB in the 60-kDa domain. We also demonstrate that mercaptoethanol, reducing impurities in glycerol, and dithioerythritol, in the presence of EDTA, replace ascorbate in the oxidative system. In addition, we study the influence of the oxidation on the degradation of the enzyme by rat liver lysosomes, mitochondria, and cytosol.
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PMID:Oxidative inactivation of carbamoyl phosphate synthetase (ammonia). Mechanism and sites of oxidation, degradation of the oxidized enzyme, and inactivation by glycerol, EDTA, and thiol protecting agents. 153 38

The arcABC operon of Pseudomonas aeruginosa encodes arginine deiminase, catabolic ornithine carbamoyltransferase and carbamate kinase, respectively. We have determined the nucleotide sequences of the arcA and arcC genes. The arcA open reading frame specifies a polypeptide of 46.3 kDa. The same molecular mass was obtained for the subunit of purified arginine deiminase after electrophoresis under denaturing conditions. The N-terminal amino acid sequence of arginine deiminase was in agreement with the corresponding nucleotide sequence. The native arginine deiminase had an estimated molecular mass of 175-180 kDa, suggesting a tetrametric structure. The enzyme was activated by Mg2+ or Mn2+ and strongly inhibited by Zn2+. The apparent Km for L-arginine was 0.04 mM in the presence of Mg2+ and 0.47 mM without Mg2+. The arcC open reading frame codes for a 33-kDa protein, confirming the molecular mass previously reported for the subunit of carbamate kinase. The translation-initiation site of arcC was determined by deletion mapping. Two regions of dyad symmetry found between arcA and arcC might stabilize the putative arcABC transcript in the upstream (arcA) region; this might contribute to the high level of arcA expression as compared to the moderate level of arcC expression. Carbamate kinase had 37% sequence similarity (and 13.5% identity) with the C-terminal part of carbamoyl-phosphate synthetase (large subunit) from Escherichia coli. Arginine deiminase had no apparent similarity with argininosuccinate lyase. Thus, the arcA and arcC genes do not appear to be closely related to arginine biosynthetic genes, whereas it had previously been shown that the arcB gene has a high degree of identity with the arginine biosynthetic argF genes of P. aeruginosa and E. coli.
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PMID:Sequence analysis and expression of the arginine-deiminase and carbamate-kinase genes of Pseudomonas aeruginosa. 253 2

Ammonia assimilation for urea synthesis by liver mitochondria in marine elasmobranchs involves, initially, formation of glutamine which is subsequently utilized for mitochondrial carbamoyl phosphate synthesis [P. M. Anderson and C. A. Casey (1984) J. Biol. Chem. 259, 456-462]. The purpose of this study was to determine if the glutamine synthetase catalyzing this first step in urea synthesis has properties uniquely related to this function. Glutamine synthetase has been highly purified from isolated liver mitochondria of Squalus acanthias, a representative elasmobranch. The purified enzyme has a molecular weight of approximately 400,000 in the presence of Mg2+, MgATP, and L-glutamate, but dissociates reversibly to a species with a molecular weight of approximately 200,000 in the absence of MgATP and L-glutamate. Association with the glutamine- and acetylglutamate-dependent carbamoyl phosphate synthetase, also located in the mitochondria, could not be demonstrated. The subunit molecular weight is approximately 46,000. The pH optimum of the biosynthesis reaction is 7.1-7.4. The purified enzyme is stabilized by MgATP and glutamate and by ethylene glycol, and is activated by 5-10% ethylene glycol. The apparent Km values for MgATP, L-glutamate, and ammonia (NH4+-NH3) are 0.7, 11.0, and 0.015 mM, respectively. Mg2+ in excess of that required to complex ATP as MgATP is required for maximal activity; Mn2+ cannot replace Mg2+. The enzyme is activated by low concentrations of chloride, bromide, or iodide; this effect appears to be related to decreases in the apparent Km for glutamate. The enzyme is inhibited by physiological concentrations of urea, but is not significantly affected by physiological concentrations of trimethylamine-N-oxide. Except for activation by halogen anions and the very low apparent Km for ammonia, this elasmobranch glutamine synthetase has properties similar to those reported for mammalian and avian glutamine synthetases. The very low apparent Km for ammonia may be specifically related to the unique role of this glutamine synthetase in mitochondrial assimilation of ammonia for urea synthesis.
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PMID:Purification and properties of glutamine synthetase from liver of Squalus acanthias. 286 Aug 71

Two paramagnetic probes, viz., Mn2+ and Cr3+-ATP, were used to map distances to various loci on carbamoyl-phosphate synthetase by using NMR measurements. The paramagnetic influence of Mn2+ on the 1H of L-glutamate and L-ornithine was measured at 200 and 360 MHz. On the basis of these data, a correlation time for the paramagnetic interaction was determined (2 X 10(-9) s) and used to compute distances. These were in the range 7-9 A. Distances were also calculated from Mn2+ to the 13C-5 atom of glutamate (8.6 A), to the monovalent cation site (approximately 8 A), and to the phosphorus atoms of ATP in the Co(NH3)4ATP complex. For studies of the monovalent cation site relaxation rates of 6Li+, 7Li+, and 15NH4+ were measured. With Cr3+ ATP as a paramagnetic substrate analogue, Cr3+ to 13C distances were measured with the substrates HCO3(-) and [5-13C]glutamate. These NMR data provide the first topographical map of the arrangement of substrates, metal ion activators, and allosteric modifiers on the Escherichia coli carbamoyl-phosphate synthetase dimer.
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PMID:A nuclear magnetic resonance study of the topography of binding sites of Escherichia coli carbamoyl-phosphate synthetase. 634 70

Carbamoyl phosphate synthetase catalyzes the formation of carbamoyl phosphate from one molecule of bicarbonate, two molecules of Mg2+ATP and one molecule of glutamine or ammonia depending upon the particular form of the enzyme under investigation. As isolated from Escherichia coli, the enzyme is an alpha,beta-heterodimer consisting of a small subunit that hydrolyzes glutamine and a large subunit that catalyzes the two required phosphorylation events. Here the three-dimensional structure of carbamoyl phosphate synthetase from E. coli refined to 2.1 A resolution with an R factor of 17.9% is described. The small subunit is distinctly bilobal with a catalytic triad (Cys269, His353 and Glu355) situated between the two structural domains. As observed in those enzymes belonging to the alpha/beta-hydrolase family, the active-site nucleophile, Cys269, is perched at the top of a tight turn. The large subunit consists of four structural units: the carboxyphosphate synthetic component, the oligomerization domain, the carbamoyl phosphate synthetic component and the allosteric domain. Both the carboxyphosphate and carbamoyl phosphate synthetic components bind Mn2+ADP. In the carboxyphosphate synthetic component, the two observed Mn2+ ions are both octahedrally coordinated by oxygen-containing ligands and are bridged by the carboxylate side chain of Glu299. Glu215 plays a key allosteric role by coordinating to the physiologically important potassium ion and hydrogen bonding to the ribose hydroxyl groups of ADP. In the carbamoyl phosphate synthetic component, the single observed Mn2+ ion is also octahedrally coordinated by oxygen-containing ligands and Glu761 plays a similar role to that of Glu215. The carboxyphosphate and carbamoyl phosphate synthetic components, while topologically equivalent, are structurally different, as would be expected in light of their separate biochemical functions.
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PMID:The structure of carbamoyl phosphate synthetase determined to 2.1 A resolution. 1008 90

The degradation of rat hepatic carbamoyl phosphate synthetase I (CPS) by calcium-activated thiol protease (calpain II) isolated from the same tissue was evaluated in vitro. Calpain was purified as a heterodimer containing subunits of 72-kDa (catalytic) and 29-kDa (regulatory). The identity of this protease as calpain II was confirmed by its dependence on calcium in the 2-4 mM range for maximal activity (525 microM calcium required for half-maximal activity) and reactivity with anti-calpain II antibody on Western blots. Calpain II was not activated (<10%) by Mg2+ or Mn2+. CPS degradation was monitored by discontinuous sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis (SDS-PAGE) and CPS fragments characterized with Western blotting with an anti-CPS antibody. Exposure of CPS (160-kDa) to calpain II resulted in the generation of single and limited degradation product of approximately 136-kDa. The smaller CPS fragment (approximately 24-kDa) appears unstable since it was not detected under these conditions. In contrast, the larger 136-kDa CPS fragment was quite stable despite extended incubation with calpain II (up to 60 min). Two-dimensional electrophoretic analysis (isoelectric focusing IEF/SDS-PAGE) revealed that the 136-kDa CPS fragment focused at more acidic isoelectric point (pI) than the parent molecule (pI range 5.95-6.35 vs 6.35-6.75, respectively). Based on the size and acidic pI shift of the degradation fragment, the calpain-susceptible site most likely involves removal of the positively-charged C-terminus of CPS. The potential significance of these findings to physiological regulation of CPS by calpain is discussed.
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PMID:Limited degradation of carbamoyl phosphate synthetase I by calcium-activated protease (calpain): electrophoretic evidence for removal of the C-terminal N-acetylglutamate regulatory domain. 1050 40