Vicente Fresquet

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Cobyrinic acid a,c-diamide synthetase from Salmonella typhimurium (CbiA) is the first glutamine amidotransferase in the anaerobic biosynthetic pathway of vitamin B(12) and catalyzes the ATP-dependent synthesis of cobyrinic acid a,c-diamide from cobyrinic acid using either glutamine or ammonia as the nitrogen source. The cbiA gene was cloned, the(More)
Carbamate kinase (CK) catalyzes the reversible reaction NH2COO- + ATP <--> NHCOOPO3(2-) + ADP, serving to synthesize ATP from carbamoyl phosphate in those microorganisms that derive energy from anaerobic arginine degradation via the arginine dihydrolase pathway. We report here the cloning and sequencing of the CK gene from Enterococcus faecalis and(More)
Carbamoyl phosphate synthetase I (CPSI) deficiency, a recessively inherited error of the urea cycle, causes life-threatening hyperammonaemia. CPSI is a multidomain 1500-residue liver mitochondrial matrix protein that is allosterically activated by N-acetyl-l-glutamate, and which synthesises carbamoyl phosphate (CP) in three steps: bicarbonate(More)
Isoaspartyl dipeptidase (IAD) is a member of the amidohydrolase superfamily and catalyzes the hydrolytic cleavage of beta-aspartyl dipeptides. Structural studies of the wild-type enzyme have demonstrated that the active site consists of a binuclear metal center positioned at the C-terminal end of a (beta/alpha)(8)-barrel domain. Steady-state kinetic(More)
Asparagine synthetase B (AsnB) catalyzes the formation of asparagine in an ATP-dependent reaction using glutamine or ammonia as a nitrogen source. To obtain a better understanding of the catalytic mechanism of this enzyme, we report the cloning, expression, and kinetic analysis of the glutamine- and ammonia-dependent activities of AsnB from Vibrio cholerae.(More)
Carbamoyl phosphate (CP), the essential precursor of pyrimidines and arginine, is made in Escherichia coli by a single carbamoyl phosphate synthetase (CPS) consisting of 41.4 and 117.7 kDa subunits, which is feed-back inhibited by UMP and activated by IMP and ornithine. The large subunit catalyzes CP synthesis from ammonia in three steps, and binds the(More)
Vitamin B12 is utilized as an essential cofactor in a wide range of enzyme-catalyzed reactions. Most of the enzymes involved in the biosynthesis of this complex macromolecule have now been identified and biochemically characterized.1 Cobyric acid synthetase (CbiP) from Salmonella typhimurium catalyzes the ATP-dependent amidation of adenosyl-cobyrinic acid(More)
Cobyric acid synthetase (CbiP) from Salmonella typhimurium catalyzes the glutamine and ATP-dependent amidation of carboxylates b, d, e, and g within adenosyl cobyrinic acid a,c-diamide. After each round of catalysis the partially amidated intermediates are released into solution and the four carboxylates are amidated in the sequential order of e, d, b, and(More)
Photoaffinity labeling with IMP was used to attach covalently this activator to its binding site of Escherichia coli carbamoyl phosphate synthetase. We now identify histidine 995 of the large enzyme subunit as the amino acid that is cross-linked with IMP. The identification was carried out by comparative peptide mapping in two chromatographic systems of(More)
Collagen IV, the major component of basement membranes, is composed of six distinct alpha chains (alpha 1-alpha 6). Atypically among the collagen IV genes, the exons encoding the carboxyl-terminal region of the human alpha 3(IV) chain undergo alternative splicing. This region has been designated as the Goodpasture antigen because of its reactivity in the(More)