title: Biochemical genetic analysis of pyrimidine biosynthesis in mammalian cells: III. Association of carbamyl phosphate synthetase, aspartate transcarbamylase, and dihydroorotase in mutants of cultured Chinese hamster cells.
abstract: Carbamyl phosphate synthetase (EC 2.7.2.9), aspartate transcarbamylase (EC 2.1.3.2), and dihydroorotase (EC 3.5.2.3), the first three enzymes in de novo pyrimidine synthesis in Chinese hamster ovary cell strain Kl (CHO-Kl), cose diment through a glycerol gradient. When an extract from Urd- A, a pyrimidine-requiring auxotroph reduced in all three activities, is run on a glycerol gradient, the enzyme activities appear in two peaks higher in the gradient, a peak of aspartate transcarbamylase separated from a peak of carbamyl phosphate synthetase and dihydroorotase. Revertants of Urd- A have increased activity of all three enzymes and give glycerol gradient patterns similar to either CHO-Kl or Urd- A. The gradient pattern for Urd- A and some of its revertants can be mimicked by treating the CHO-Kl cell extract with trypsin. Hybrids made between a CHO-Kl purine-requiring auxotroph (Ade- C) and a Urd- A revertant gave a glycerol gradient pattern which is a composite of the CHO-Kl and revertant patterns. A model is presented for the structure of this multifunctional protein.
mesh_terms: D000581:Amidohydrolases / Q000032:analysis*; D000818:Animals; D001221:Aspartate Carbamoyltransferase / Q000032:analysis*; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000032:analysis*; D002460:Cell Line; D002850:Chromatography, Gel; D006224:Cricetinae; D004080:Dihydroorotase / Q000032:analysis*; D005260:Female; D008956:Models, Chemical; D009097:Multienzyme Complexes / Q000235:genetics*; D009154:Mutation; D010053:Ovary; D010770:Phosphotransferases / Q000032:analysis*; D011487:Protein Conformation
chemical_list: D009097:Multienzyme Complexes; D001221:Aspartate Carbamoyltransferase; D010770:Phosphotransferases; D000581:Amidohydrolases; D004080:Dihydroorotase; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)