title: Efflux and the steady state in alpha-methylglucoside transport in Escherichia coli.
abstract: Efflux and the steady state in a group translocation system, the alpha-methylglucoside (alphaMG) transport system, were investigated. The maximum intracellular level of alpha-methylglucoside is a function of a steady state. There is no inhibition of alphaMG influx as the intracellular pool of alphaMG, and alpha-methylglucoside-6-phosphate (alphaMGP) rises. This steady state has three components: alphaMG influx, action of an alphaMGP phosphatase, and alphaMG efflux. The phosphatase is the rate-limiting step (half-time = 5.0 min); thus, the true efflux rate (half-time = 2.0 min) cannot be simply measured from the kinetics of alphaMG loss from the cell. Under our steady-state conditions the percentage of intracellular radioactivity present as alphaMGP was 71%. Under conditions of zero influx, after an efflux of 12 min the percentage present as alphaMGP fell to 55%. However, when fluoride was present during the efflux period, the percentage of the sugar as alphaMGP increased to about 85%. Fluoride greatly inhibits both influx and phosphatase activity (half-time = 50 min). The efflux of alphaMG from the cell is apparently also fluoride-sensitive but to a lesser extent (half-time = 4.1 min). These data are summarized in a model describing the three components of the steady-state and effect of fluoride.
mesh_terms: D001386:Azides / Q000494:pharmacology; D002247:Carbon Isotopes; D003201:Computers; D003470:Culture Media; D004579:Electron Transport / Q000187:drug effects; D004926:Escherichia coli / Q000032:analysis / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D005374:Filtration; D005459:Fluorides / Q000494:pharmacology; D005990:Glycerol; D006027:Glycosides / Q000032:analysis / Q000378:metabolism*; D008745:Methylation; D008962:Models, Theoretical; D010710:Phosphates / Q000032:analysis; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014867:Water / Q000032:analysis
chemical_list: D001386:Azides; D002247:Carbon Isotopes; D003470:Culture Media; D006027:Glycosides; D010710:Phosphates; D014867:Water; D010744:Phosphoric Monoester Hydrolases; D005990:Glycerol; D005459:Fluorides