Publications

• Carbamate kinase: new structural machinery for making carbamoyl phosphate, the common precursor of pyrimidines and arginine.

  Marina A., Alzari P.M., Bravo J., Uriarte M., Barcelona B., Fita I., Rubio V.

  The enzymes carbamoyl phosphate synthetase (CPS) and carbamate kinase (CK) make carbamoyl phosphate in the same way: by ATP-phosphorylation of carbamate. The carbamate used by CK is made chemically, whereas CPS itself synthesizes its own carbamate in a process involving the phosphorylation of bica ... >> More

  The enzymes carbamoyl phosphate synthetase (CPS) and carbamate kinase (CK) make carbamoyl phosphate in the same way: by ATP-phosphorylation of carbamate. The carbamate used by CK is made chemically, whereas CPS itself synthesizes its own carbamate in a process involving the phosphorylation of bicarbonate. Bicarbonate and carbamate are analogs and the phosphorylations are carried out by homologous 40 kDa regions of the 120 kDa CPS polypeptide. CK can also phosphorylate bicarbonate and is a homodimer of a 33 kDa subunit that was believed to resemble the 40 kDa regions of CPS. Such belief is disproven now by the CK structure reported here. The structure does not conform to the biotin carboxylase fold found in the 40 kDa regions of CPS, and presents a new type of fold possibly shared by homologous acylphosphate-making enzymes. A molecular 16-stranded open beta-sheet surrounded by alpha-helices is the hallmark of the CK dimer. Each subunit also contains two smaller sheets and a large crevice found at the location expected for the active center. Intersubunit interactions are very large and involve a central hydrophobic patch and more hydrophilic peripheral contacts. The crevice holds a sulfate that may occupy the site of an ATP phosphate, and is lined by conserved residues. Site-directed mutations tested at two of these residues inactivate the enzyme. These findings support active site location in the crevice. The orientation of the crevices in the dimer precludes their physical cooperation in the catalytic process. Such cooperation is not needed in the CK reaction but is a requirement of the mechanism of CPSs. << Less

  Protein Sci. 8:934-940(1999) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Fermentative arginine degradation in Halobacterium salinarium (formerly Halobacterium halobium): genes, gene products, and transcripts of the arcRACB gene cluster.

  Ruepp A., Soppa J.

  Fermentative growth via the arginine deiminase pathway is mediated by the enzymes arginine deiminase, carbamate kinase, and catabolic ornithine transcarbamylase and by a membrane-bound arginine-ornithine antiporter. Recently we reported the characterization of catabolic ornithine transcarbamylase ... >> More

  Fermentative growth via the arginine deiminase pathway is mediated by the enzymes arginine deiminase, carbamate kinase, and catabolic ornithine transcarbamylase and by a membrane-bound arginine-ornithine antiporter. Recently we reported the characterization of catabolic ornithine transcarbamylase and the corresponding gene, arcB, from Halobacterium salinarium (formerly Halobacterium halobium). Upstream of the arcB gene, three additional open reading frames with halobacterial codon usage were found. They were identified as the arcC gene coding for carbamate kinase, the arcA gene coding for arginine deiminase, and a gene, tentatively termed arcR, coding for a putative regulatory protein. The identification of the arcC and arcA genes was verified, respectively, by heterologous expression of the enzyme in Haloferax volcanii and by protein isolation and N-terminal sequence determination of three peptides. The gene order arcRACB differs from the gene order arcDABC in Pseudomonas aeruginosa, the only other organism for which sequence information is available. Transcripts from H. salinarium cultures grown fermentatively or aerobically were characterized by Northern (RNA) blot and primer extension analyses. It was determined (i) that monocistronic transcripts corresponding to the four open reading frames exist and that there are three polycistronic transcripts, (ii) that the level of induction during fermentative growth differs for the various transcripts, and (iii) that upstream of the putative transcriptional start sites for the three structural genes there are sequences with similarities to the halobacterial consensus promoter. The data indicate that expression of the arc gene cluster and its regulation differ in H. salinarium and P. aeruginosa. << Less

  J. Bacteriol. 178:4942-4947(1996) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Histochemical studies of bone marrow cells in kwashiorkor.

  Khalil M., Kassem A.S., Hafez M., Mehareb S.W., Girgis R., El Sawy M.

  J Trop Pediatr Environ Child Health 23:103-107(1977) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Crystalline carbamate kinase.

  Bishop S.H., Grisolia S.

  Biochim Biophys Acta 118:211-215(1966) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Enzymic conversion of agmatine to putrescine in Lathyrus sativus seedlings. Purification and properties of a multifunctional enzyme (putrescine synthase).

  Srivenugopal K.S., Adiga P.R.

  The participation of a multifunctional enzyme (a single polypeptide with multiple catalytic activities (14)) has been demonstrated in the conversion of agmatine to putrescine in Lathyrus sativus seedlings. This enzyme (putrescine synthase) with inherent activities of agmatine iminohydrolase, putre ... >> More

  The participation of a multifunctional enzyme (a single polypeptide with multiple catalytic activities (14)) has been demonstrated in the conversion of agmatine to putrescine in Lathyrus sativus seedlings. This enzyme (putrescine synthase) with inherent activities of agmatine iminohydrolase, putrescine transcarbamylase, ornithine transcarbamylase, and carbamate kinase has been purified to homogeneity and has Mr = 55,000. In the presence of inorganic phosphate, the enzyme catalyzed the stoichiometric conversion of agmatine and ornithine to putrescine and citrulline, respectively. The different activities associated with the enzyme copurified with near constancy in their specific activity. The enzyme catalyzed phosphorolysis and arsenolysis of N-carbamyl putrescine. The multifunctionality of putrescine synthase was also supported by 1) activity staining, 2) intact transfer of the ureido-14C group from labeled NJ-carbamyl putrescine to ornithine to form citrulline, and 3) the affinity of the enzyme toward structurally and functionally related affinity matrices. An agmatine cycle is proposed wherein N-carbamyl putrescine arising from the agmatine iminohydrolase reaction is converted to putrescine and citrulline, with the ureido group of N-carbamyl putrescine being transferred intact to ornithine. Preliminary results indicate that this series of reactions is also present in other plants. << Less

  J Biol Chem 256:9532-9541(1981) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.