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  • Title: On the rate limiting step in downhill transport via the LacY permease of Escherichia coli.
    Author: Rotman B.
    Journal: J Supramol Struct; 1977; 7(1):29-35. PubMed ID: 415184.
    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.
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