IMPAIRED GROWTH OF AN ESCHERICHIA-COLI RPE MUTANT LACKING RIBULOSE-5-PHOSPHATE EPIMERASE ACTIVITY

We present evidence that ribulose-5-phosphate epimerase, a central met abolic enzyme acting in the non-oxidative branch of the pentose-phosph ate pathway, is encoded by a gene in the dam containing operon of Esch erichia coli. Enzymatic assays confirm that this gene encodes ribulose -5-phosphate epimerase activity. Disruption of the gene (rpe) causes l oss of enzymatic activity and renders the rpe mutant unable to utilize single pentose sugars, indicating that rpe supplies the only ribulose -5-phosphate epimerase activity in E. coli. Growth of the rpe mutant i s impaired in complex LB medium and severely impaired in minimal mediu m containing glycolytic carbon sources or gluconate. Enrichment with c asamino acids abolishes or strongly relieves growth suppression in min imal medium. Aspartate counteracts the impaired growth in glycolytic c arbon sources but not in gluconate. We suggest that the absence of the Rpe enzyme causes changes in the pentose-phosphate levels which alter the regulation of (a) metabolic enzyme(s) and thereby cause growth su ppression and that the severity of growth suppression is related to th e internal concentration of pentose-phosphates. Target enzymes for neg ative regulation may be located in the early parts of the Embden-Meyer hof-Parnas pathway and of the Entner-Doudoroff pathway and/or of carbo hydrate transport systems feeding sugars into these sections of centra l metabolic pathways. (C) 1998 Elsevier Science B.V. All rights reserv ed.