title: [Mechanisms of efflux of a substrate accumulated by the lactose permease of Escherichia coli: theoretical and experimental study].
abstract: At the steady-state of accumulation of intracellular lactose by the beta-galactoside permease of Escherichia coli, the rate of efflux of the substrate is equal to its rate of influx. An original experimental method and a mathematical processing of the experimental data are proposed to evaluate the relative involvements of the permease-mediated pathway and of the diffusion component in this efflux. The method consists of inducing the lac operon of the bacteria, and then of removing the inducer and allowing the cells to grow further. The permease content and the membrane surface of diffusion are thus varying independently in such a "de-induction" experiment, along which lactose uptake has been monitored at different times. The analysis of the experimental data show that, under conditions of maximal induction, over 95% of the efflux passes through the energized permease. The relevant parameters of the efflux of lactose have been computed and their values allow the prediction of most classical observations, as well as the prediction, never checked, that under physiological conditions, the higher the external substrate concentration, the higher the permease-mediated efflux, according to a saturation kinetics.
mesh_terms: D001692:Biological Transport; D004058:Diffusion; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007700:Kinetics; D007763:Lac Operon; D007785:Lactose / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D027981:Symporters
chemical_list: D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease; D007785:Lactose
vernacular_title: Mécanismes d'efflux d'un substrat accumulé par la lactose perméase de Escherichia coli: étude théorique et expérimentale.