title: On the rate limiting step in downhill transport via the LacY permease of Escherichia coli.
abstract: Strains of Escherichia coli K12 were constructed for the specific purpose of evaluating the inducibility of the influx mechanism controlled by the lacY gene. These strains are heteromerodiploids characterized by a high and relatively constant level of beta-D-galactosidase which is not affected significantly by induction of the Lac operon. These properties were obtained by introducing episomal lacI+,Oc,Z+,Y-genes into the cells. In these merodiploids the rate of o-nitrophenyl-beta-D-galactopyranoside (ONPG) hydrolysis of extracted cells is 50-times that of intact cells. This difference indicates that the rate limiting step in the ONPG hydrolysis by intact cells is influx. Using a set of merodiploids with and without the LacY transport system, we were able to demonstrate a specific induction of ONPG influx. However, the increase in influx due to induction was only 3.5-fold as compared to the 40-fold increase observed when the LacY permease was measured by intracellular accumulation of [14C]TMG.
mesh_terms: D001692:Biological Transport; D004790:Enzyme Induction; D004926:Escherichia coli / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism*; D006868:Hydrolysis; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009598:Nitrophenylgalactosides / Q000378:metabolism*; D010957:Plasmids; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D006027:Glycosides; D026901:Membrane Transport Proteins; D009598:Nitrophenylgalactosides; D001616:beta-Galactosidase