title: Factors accelerating pyrimidine production in Deinococcus radiophilus.
abstract: In studying the pyrimidine synthesising pathway in Deinococcus radiophilus two instances of anomalous behaviour were observed. One was the strikingly different results obtained for two types of assay for carbamoyl phosphate synthetase. Both depend on the fixation of 14C from the substrate bicarbonate to give radioactive products. In the coupled assay the carbamoyl phosphate product of the enzyme is converted to carbamoyl aspartate in the presence of aspartate and aspartate transcarbamoylase. In the direct assay aspartate is omitted from the reaction mixture and the carbamoyl phosphate is converted to urea. It was found that the radioactive counts in the direct assay were about 5% of those measured in the coupled assay. The second anomaly was that omission of glutamine from both assay mixtures had no significant effect on the fixation of radioactive carbon. These results suggested that aspartate amino-N could be the source of nitrogen for glutamine synthesis by a substrate-channelled pathway which delivered glutamine to carbamoyl phosphate synthetase, and that externally added glutamine could not access its binding site on the enzyme.
authors.affiliation: School of Life Sciences, University of the West of England, Coldharbour Lane, Bristol, BS16 1QY, UK.
authors.forename: Don
authors.initials: D
authors.lastname: McPhail
authors.forename: Man-Kim
authors.initials: MK
authors.lastname: Cheung
authors.forename: Judith
authors.initials: J
authors.lastname: Brown
authors.forename: Margaret
authors.initials: M
authors.lastname: Shepherdson
mesh_terms: D001221:Aspartate Carbamoyltransferase / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D002221:Carbamyl Phosphate / Q000378:metabolism; D034301:Deinococcus / Q000737:chemistry* / Q000201:enzymology / Q000378:metabolism*; D000090722:Dihydroorotate Dehydrogenase; D005973:Glutamine / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D000090722:Dihydroorotate Dehydrogenase; D011743:Pyrimidines; D005973:Glutamine; D002221:Carbamyl Phosphate; D044925:Oxidoreductases Acting on CH-CH Group Donors; D001221:Aspartate Carbamoyltransferase; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing); C030986:pyrimidine