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

1. The influence of ammonia and ornithine on the oxygen uptake and the formation of citrulline was investigated with isolated rat liver mitochondria. The experiments were performed in a cytosol-like saline medium at 38 degrees C. 2. Under these conditions an increase of the respiration rate by ammonia and ornithine was observed, but a small response to external ADP, only. The missing stimulation by ADP was due to a partial inhibition of the respiratory chain by traces of zinc (approximately 1 microM) present in the medium. This inhibition was only detected at low concentrations of mitochondria. 3. For activation of respiration by ammonia plus ornithine two different processes were responsible: (i) chelation of the inhibiting zinc by ornithine, which could be prevented by EDTA; (ii) ADP production in the matrix space during formation of carbamoyl phosphate, which could be prevented by oligomycin but not by carboxyatractyloside. 4. This stimulus of the carbamoyl phosphate formation and of the equivalent citrulline synthesis on the mitochondrial respiration ran to 12% of that increase caused by phosphorylation of external ADP. The maximum rate of citrulline formation was limited by the activity of carbamoyl phosphate synthetase. 5. Added ADP suppresses the production of citrulline probably by the exchange of extramitochondrial ADP versus intramitochondrial ATP. The data suggest a common adenine nucleotide pool delivering ATP to the adenine nucleotide translocase as well as to the carbamoyl phosphate synthetase.
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PMID:The stimulation of the mitochondrial respiration by citrulline synthesis. 11 92

Perfusion of rat liver had led to the suggestion that oxygen tension, rather than the distribution of enzymes of urea synthesis, plays a key role in the regulation of urea synthesis in the periportal and pericentral areas of the liver lobule [F. W. Kari, H. Yoshihara and R. G. Thurman (1987) Eur. J. Biochem. 163, 1-7]. We have directly tested the effect of oxygen concentration on ureogenesis under steady-state conditions in isolated hepatocytes perifused with physiological concentrations of ammonia. We found that ureogenesis is independent of the oxygen concentration. Only at oxygen concentrations below 25 microM (which is below the oxygen concentration in liver) was urea synthesis decreased. This was because insufficient production of ATP led to decreased flux through carbamoyl-phosphate synthase. It is concluded that oxygen does not control urea synthesis.
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PMID:Oxygen tension does not affect urea synthesis in perifused rat hepatocytes. 199 25

Of the two mitochondrial enzymes of the urea cycle, carbamoyl phosphate synthetase (CPS) was and ornithine transcarbamylase (OTC) was not inactivated by the Fe3+-oxygen-ascorbate model system for mixed-function oxidation [R. L. Levine, (1983) J. Biol. Chem. 258, 11828-11833]. The susceptibility of OTC was not increased by its substrates, products, or inhibitors, whereas that of CPS was markedly increased by acetylglutamate (its allosteric activator) when ATP was absent. Thus, acetylglutamate binds in the absence of ATP and exposes to oxidation essential groups of the enzyme. We estimate for this binding a KD value of 1.6 mM, which greatly exceeds the KD values (less than 10 microM) determined in the presence of ATP and bicarbonate. ATP, and even more, mixtures of ATP and bicarbonate protected CPS from inactivation. Acetylglutamate exposes the site for the ATP molecule that yields Pi, and it appears that ATP protects by binding at this site. Experiments of limited proteolysis with elastase suggest that oxidation prevents this binding of ATP and show that it accelerates cleavage of CPS by the protease, thus supporting the idea that oxidation may precede proteolysis. Trypsin, chymotrypsin, and papain also hydrolyze the oxidized enzyme considerably faster than the native enzyme. Our results also support the idea that oxidative inactivation is site specific and requires sites on the enzyme for Me2+ and, possibly, for a nucleotide.
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PMID:Inactivation of mitochondrial carbamoyl phosphate synthetase induced by ascorbate, oxygen, and Fe3+ in the presence of acetylglutamate: protection by ATP and HCO3- and lack of inactivation of ornithine transcarbamylase. 282 12

The activities of key glutamine and urea cycle enzymes were assayed in liver homogenates from control and chronically acidotic rats and compared with citrulline and urea productions by isolated mitochondria and intact liver slices, respectively. Glutamine-dependent urea and citrulline synthesis were increased significantly in isolated mitochondria and in liver slices; the activities of carbamoyl phosphate synthetase and arginase were unchanged and increased, respectively. Glutamine was not a precursor in the carbamoyl phosphate synthetase system, suggesting that the glutamine effect is an indirect one and that glutamine requires prior hydrolysis. Increased mitochondrial citrulline synthesis was associated with enhanced oxygen consumption, suggesting glutamine acts both as a nitrogen and fuel source. Hepatic phosphate-dependent glutaminase was elevated by chronic acidosis. The results indicate that the acidosis-induced reduction in ureagenesis and reversal from glutamine uptake to release observed in vivo are not reflections of corresponding changes in the hepatic enzyme content. Rather, when available, glutamine readily supports ureagenesis, suggesting a close coupling of hepatic glutaminase flux with citrulline synthesis.
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PMID:Hepatic enzymes of glutamine and ureagenesis in metabolic acidosis. 287 77

Plasma fibronectin (FN) has been demonstrated to serve as an opsonin involved in the ingestion of foreign particles by phagocytes. This study concerns the effect of FN exposure on the respiratory burst of normal human peripheral phagocytes, using a luminol-dependent chemiluminescence (CL) assay for measurement of reactive oxygen metabolites generated. FN enhanced, in a dose-dependent manner, the CL response of circulating monocytes stimulated, probably via beta-glucan receptor, with unopsonized zymosan. FN also increased the CL response of phagocytes to fresh serum-opsonized zymosan. When we used a glycolipid (ceramide pentasaccharide, CPS) incorporated on liposome membranes as an antigen, the immune complexes prepared between CPS and human IgG (as antibody) did not induce a CL response, differing from previous reports. Addition of FN to the immune complexes significantly enhanced the CL response of phagocytes. The role of FN in host defence is discussed.
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PMID:Fibronectin enhances respiratory burst of phagocytes stimulated by zymosan and immune complexes. 319 70

The kinetic mechanism of carbamoyl-phosphate synthetase II from Syrian hamster kidney cells has been determined at pH 7.2 and 37 degrees C. Initial velocity, product inhibition, and dead-end inhibition studies of both the biosynthetic and bicarbonate-dependent adenosinetriphosphatase (ATPase) reactions are consistent with a partially random sequential mechanism in which the ordered addition of MgATP, HCO3-, and glutamine is followed by the ordered release of glutamate and Pi. Subsequently, the binding of a second MgATP is followed by the release of MgADP, which precedes the random release of carbamoyl phosphate and a second MgADP. Carbamoyl-phosphate synthetase II catalyzes beta gamma-bridge:beta-nonbridge positional oxygen exchange of [gamma-18O]ATP in both the ATPase and biosynthetic reactions. Negligible exchange is observed in the strict absence of HCO3- (and glutamine or NH4+). The ratio of moles of MgATP exchanged to moles of MgATP hydrolyzed (nu ex/nu cat) is 0.62 for the ATPase reaction, and it is 0.39 and 0.16 for the biosynthetic reaction in the presence of high levels of glutamine and NH4+, respectively. The observed positional isotope exchange is suppressed but not eliminated at nearly saturating concentrations of either glutamine or NH4+, suggesting that this residual exchange results from either the facile reversal of an E-MgADP-carboxyphosphate-Gln(NH4+) complex or exchange within an E-MgADP-carbamoyl phosphate-MgADP complex, or both. In the 31P NMR spectra of the exchanged [gamma-18O]ATP, the distribution patterns of 16O in the gamma-phosphorus resonances in all samples reflect an exchange mechanism in which a rotationally unhindered molecule of [18O3, 16O]Pi does not readily participate. These results suggest that the formation of carbamate from MgATP, HCO3-, and glutamine proceeds via a stepwise, not concerted mechanism, involving at least one kinetically competent covalent intermediate, such as carboxyphosphate.
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PMID:Carbamoyl-phosphate synthetase II of the mammalian CAD protein: kinetic mechanism and elucidation of reaction intermediates by positional isotope exchange. 330 Jul 76

A portable emergency bypass system using a membrane oxygenator device (CPS) was evaluated. The ability of the CPS to supply the oxygen transfer needs of five anesthetized dogs consistently over six hours and the system's effects on hemoglobin concentration, platelet count, and degree of hemolysis were assessed. The animals maintained spontaneous heart beats, pump flows averaged 100 ml/kg/min; mean arterial pressures were maintained at from 114 to 144 mm Hg. Immediate dilution of hemoglobin and platelet levels occurred in the first 30 minutes. Further hemodilution was limited during the first two hours, although three of the animals required transfusions during the six-hour period to maintain their hematocrits. Plasma free hemoglobin did not significantly increase during the six hours. Baseline oxygen consumption data obtained in three animals ranged from 44.5 to 96 (ml oxygen/min/m2). Oxygen and carbon dioxide transfer measurements during the first hour of bypass were not significantly different from measurements during the last hour of perfusion. The study suggests that optimal use of the CPS could supply much if not all of a patient's basal oxygen transfer requirements for at least six hours.
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PMID:Emergency bypass system: analysis of gas transfer. 381 78

The mechanism of the reaction catalyzed by rat liver mitochondrial carbamoyl-phosphate synthetase has been studied by using [beta-18O2]ATP and HC18O-3, monitoring the isotopic composition of adenosine triphosphate (ATP) and inorganic phosphate (Pi) by high-resolution 31P NMR spectroscopy. In the presence of both HCO3- and acetylglutamate, the enzyme catalyzes the exchange of oxygen atoms between the beta, gamma bridging and the beta nonbridging positions of ATP. Addition of NH3 stops the exchange, Pi released by the ATPase activity of the enzyme in the absence of NH3 contains one oxygen atom from HC18O3- but there is no incorporation of 18O into ATP. There is no significant incorporation of [14C]ADP or 32Pi into ATP. It is concluded that in the enzyme-ATPA.HCO30.ATPB complex formed in the presence of ATP and HCO3- there is reversible transfer of the gamma-PO3 group of ATPA (the molecule that yields Pi) to HCO3- without dissociation of products. The beta-PO3 of the enzyme-bound ADP that is formed can rotate. Virtually all of the complex appears to be in the form in which ATPA is cleaved, but in the absence of NH3, ATP is reconstituted and dissociates from the complex on at least 75% of the occasions. On the remainder, the carbonyl phosphate is cleaved in an irreversible process that yields Pi and a low-energy form of carbonic acid (probably HCO3-). NH3 reacts rapidly and irreversibly with the complex, and at saturation the rate (greater than 10 times the rate of Pi release in the absence of NH3) is sufficient to prevent dissociation of ATPA. In the absence of HCO3- an enzyme-ATPA.ATPB complex is formed, but cleavage of the bond between beta, gamma bridging oxygen and P gamma of ATPA does not occur.
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PMID:Mechanism of activation of bicarbonate ion by mitochondrial carbamoyl-phosphate synthetase: formation of enzyme-bound adenosine diphosphate from the adenosine triphosphate that yields inorganic phosphate. 626 8

The synthesis of citrulline from glutamine was quantified in enterocytes from pre-weaning (14-21 days old) and post-weaning (29-58 days old) pigs. The cells were incubated at 37 degrees C for 30 min in Krebs-Henseleit bicarbonate buffer (pH 7.4) containing 0, 0.5, 2 and 5 mM glutamine. Oxygen consumption was linear during the 30 min incubation period. The rates of citrulline synthesis were low or negligible in enterocytes from 14-21-day-old pigs, but increased 10-20-fold in the cells from 29-58-day-old pigs. This marked elevation of citrulline synthesis coincided with an increase in the activity of pyrroline-5-carboxylate synthase with the animal's post-weaning growth. In contrast, decreases in the activities of phosphate-dependent glutaminase, ornithine aminotransferase, ornithine carbamoyltransferase and carbamoyl-phosphate synthase were observed as the age of the pigs increased. The concentrations of carbamoyl phosphate in enterocytes from pre-weaning pigs were higher than, or similar to, those in the cells from post-weaning pigs. It is possible that the low rate of citrulline synthesis from glutamine in enterocytes from pre-weaning pigs was due to a limited availability of ornithine, rather than that of carbamoyl phosphate. We suggest that this limited availability of ornithine in pre-weaning-pig enterocytes results from (i) the low rate of pyrroline-5-carboxylate synthesis from glutamate, due to the low activity of pyrroline-5-carboxylate synthase, and (ii) the competitive conversion of pyrroline-5-carboxylate into proline. Our present findings on the developmental aspect of citrulline synthesis in pig enterocytes may offer a biochemical mechanism for the previous observations that arginine is a nutritionally essential amino acid for suckling piglets, but not for adult pigs.
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PMID:Synthesis of citrulline from glutamine in pig enterocytes. 816 28

Surgical implant finishing and sterilization procedures were investigated to determine surface characteristics of unalloyed titanium (Ti). All specimens initially were cleaned with phosphoric acid and divided into five groups for comparisons of different surface treatments (C = cleaned as above, no further treatment; CP = C and passivated in nitric acid; CPS = CP and dry-heat sterilized; CPSS = CPS and resterilized; CS = C and dry-heat sterilized). Auger (AES), X-ray photoelectron (XPS), and Raman spectroscopic methods were used to examine surface compositions. The surface oxides formed by all treatments primarily were TiO2, with some Ti2O3 and possibly TiO. Significant concentrations of carbonaceous substances also were observed. The cleaning procedure alone resulted in residual phosphorus, primarily as phosphate groups along with some hydrogen phosphates. A higher percentage of physisorbed water appeared to be associated with the phosphorus. Passivation (with HNO3) alone removed phosphorus from the surface; specimens sterilized without prior passivation showed the thickest oxide and phosphorus profiles, suggesting that passivation alters the oxide characteristics either directly by altering the oxide structure or indirectly by removing moieties that alter the oxide. Raman spectroscopy showed no crystalline order in the oxide. Carbon, oxygen, phosphorus, and nitrogen presence were found to correlate with previously determined surface energy.
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PMID:Effect of surface treatment on unalloyed titanium implants: spectroscopic analyses. 959 42


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