title: Characterization of an inducible porter required for L-proline catabolism by Escherichia coli K12.
abstract: L-Proline can serve as sole source of carbon and nitrogen for the growth of Escherichia coli K12 and other Enterobacteria. L-Proline uptake and L-proline oxidase are subject both to catabolite repression and to specific induction by L-proline or glycyl-L-proline, although their regulation is not strictly coordinate. A strain defective for L-proline uptake due to a lesion at the locus putP does not show elevated uptake activity either on relief of catabolite repression or when grown on glycyl-L-proline as nitrogen source. The apparent Km for L-proline uptake decreases up to 14-fold as uptake Vm increases when cells are induced for both L-proline uptake and L-proline oxidase; cells with increased uptake activity, alone, do not show an altered Km. Although L-proline is metabolized during the uptake measurements, uptake is always active. The observed variations in uptake Km are unlikely to result from the escape of radioactive L-proline metabolites or from reversal of the transport reaction during the uptake measurements. We conclude that the L-proline porter encoded in putP is responsible for 80 to 90% of the constitutive and for the inducible L-proline uptake activity of wild-type bacteria. Although this porter is amplified in cells induced for L-proline catabolism, the observed values for uptake Vm may not be taken as a direct indicator of porter concentration.
mesh_terms: D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D010641:Phenotype; D011392:Proline / Q000378:metabolism*; D011394:Proline Oxidase / Q000378:metabolism; D014161:Transduction, Genetic
chemical_list: D002352:Carrier Proteins; D011392:Proline; D011394:Proline Oxidase