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)

A correlation was found between mitochondrial matrix free magnesium ([Mg2+]m), measured by means of the fluorescent indicator Mag-Fura-2, and citrulline synthesis in rat liver mitochondria. The variation of [Mg2+]m from 0.05 to 1.7 mM by changes in external Mg2+, induced a 20 +/- 8.5% increase in the rate of citrulline synthesis, whereas a further increase of [Mg2+]m to 3.3 mM induced a return to basal values. The increase in [Mg2+]m, as well as the diminution of external pH, also promoted an elevation of matrix free Ca2+ ([Ca2+]m). An increase in [Ca2+]m, at constant [Mg2+]m and pH, resulted in a 3-fold stimulation of citrulline synthesis. The data suggest that [Mg2+]m may modulate the rate of citrulline synthesis through a direct interaction with carbamoyl-phosphate synthase I (ammonia) and, indirectly, by changing the levels of matrix Ca2+.
 ...
PMID:Effect of intramitochondrial Mg2+ on citrulline synthesis in rat liver mitochondria. 904 47

In animals, UTP feedback inhibition of carbamyl phosphate synthetase II (CPSase) controls pyrimidine biosynthesis. Suppressor of black (Su(b) or rSu(b)) mutants of Drosophila melanogaster have elevated pyrimidine pools, and this mutation has been mapped to the rudimentary locus. We report that rSu(b) is a missense mutation resulting in a glutamate to lysine substitution within the second ATP binding site (i.e. CPS.B2 domain) of CPSase. This residue corresponds to Glu780 in the Escherichia coli enzyme (Glu1153 in hamster CAD) and is universally conserved among CPSases. When a transgene expressing the Glu-->Lys substitution was introduced into Drosophila lines homozygous for the black mutation, the resulting flies exhibited the Su(b) phenotype. Partially purified CPSase from rSu(b) and transgenic flies carrying this substitution exhibited a dramatic reduction in UTP feedback inhibition. The slight UTP inhibition observed with the Su(b) enzyme in vitro was due mainly to chelation of Mg2+ by UTP. However, the Km values for glutamate, bicarbonate, and ATP obtained from the Su(b) enzyme were not significantly different from wild-type values. From these experiments, we conclude that this residue plays an essential role in the UTP allosteric response, probably in propagating the response between the effector binding site and the ATP binding site. This is the first CPSase mutation found to abolish feedback inhibition without significantly affecting other enzyme catalytic parameters.
 ...
PMID:A mutation that uncouples allosteric regulation of carbamyl phosphate synthetase in Drosophila. 1008 Aug 91

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.
 ...
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

Carbapenam synthetase (hereafter named CPS) catalyzes the formation of the beta-lactam ring in the biosynthetic pathway to (5R)-carbapen-2-em-3-carboxylate, the simplest of the carbapenem antibiotics. Kinetic studies showed remarkable tolerance to substrate stereochemistry in the turnover rate but did not distinguish between chemistry and a nonchemical step such as product release or conformational change as being rate-determining. Also, X-ray structural studies and modest sequence homology to beta-lactam synthetase, an enzyme that catalyzes the formation of a monocyclic beta-lactam ring in a similar ATP/Mg2+-dependent reaction, implicate K443 as an essential residue for substrate binding and intermediate stabilization. In these experiments, we use pH-rate profiles, deuterium solvent isotope effects, and solvent viscosity measurements to examine the rate-limiting step in this complex overall process of substrate adenylation and intramolecular ring formation. Mutagenesis and chemical rescue demonstrate that K443 is the general acid visible in the pH-rate profile of the wild-type CPS-catalyzed reaction. On the basis of these results, we propose a mechanism in which the rate-limiting step is beta-lactam ring formation coupled to a protein conformational change and underscore the role of K443 throughout the reaction.
 ...
PMID:Rate-limiting steps and role of active site Lys443 in the mechanism of carbapenam synthetase. 1765 87


<< Previous 1 2 3