title: Biochemical genetics of Chinese hamster cell mutants with deviant purine metabolism: characterization of Chinese hamster cell mutants defective in phosphoribosylpyrophosphate amidotransferase and phosphoribosylglycinamide synthetase and an examination of alternatives to the first step of purine biosynthesis.
abstract: Activities of the first three enzymes in the de novo purine biosynthetic pathway have been measured in cell-free extracts of the Chinese hamster ovary cell (CHO-K1) and two purine-requiring auxotrophs of this cell. Ade-A has been found to be defective in phosphoribosylpryophosphate (PRPP) amidotransferase while Ade-C has been found to be defective in glycinamide ribonucleotide (GAR) synthetase. Neither enzyme deficiency is due to the presence of an excess of diffusible inhibitor, and mixed extracts of Ade-A and Ade-C are capable of performing both enzymatic steps in a coupled assay. Assays of GAR formyltransferase show that it is present in Ade-A and Ade-C, indicating that these cell types are defective in only one enzyme each of the early purine biosynthetic enzymes. Using the Ade-A mutant, analysis of alternatives to PRPP plus glutamine as substrates for the first step in the purine biosynthetic pathway showed that a common genetic unit must direct the synthesis for both PRPP plus glutamine and PRPP plus ammonia activities. Although ribose-5-phosphate plus ammonia can be used in cell-free extracts to perform the first step in purine biosynthesis, it is shown that this activity is apparently not used by intact CHO-K1 cells.
mesh_terms: D000582:Amidophosphoribosyltransferase / Q000235:genetics* / Q000378:metabolism; D000588:Amines / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D008025:Ligases / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010430:Pentosyltransferases / Q000235:genetics*; D011687:Purines / Q000096:biosynthesis*; D012267:Ribosemonophosphates / Q000378:metabolism
chemical_list: D000588:Amines; D011687:Purines; D012267:Ribosemonophosphates; D010430:Pentosyltransferases; D000582:Amidophosphoribosyltransferase; D008025:Ligases