title: Beta-galactoside transport in bacterial membrane preparations: energy coupling via membrane-bounded D-lactic dehydrogenase.
abstract: The transport of beta-galactosides by isolated membrane preparations from Escherichia coli strains containing a functional y gene is markedly stimulated by the conversion of D-lactate to pyruvate. The addition of D-lactate to these membrane preparations produces a 19-fold increase in the initial rate of uptake and a 10-fold stimulation of the steady-state level of intramembranal lactose or thiomethylgalactoside. Succinate, DL-alpha-hydroxybutyrate, and L-lactate partially replace D-lactate, but are much less effective; ATP and P-enolpyruvate, in addition to a number of other metabolites and cofactors, do not stimulate lactose transport by the vesicles. Lactose uptake by the membrane preparations in the presence of D-lactate requires oxygen, and is blocked by electron transport inhibitors and proton conductors; however, uptake is not significantly inhibited by high concentrations of arsenate or oligomycin. Furthermore, the P-enolpyruvate-P-transferase system is not involved in beta-galactoside transport by the E. coli membrane vesicles. The findings indicate that the beta-galactoside uptake system is coupled to the membrane-bound D-lactic dehydrogenase via an electron transport chain but does not involve oxidative phosphorylation.
mesh_terms: D000085:Acetates / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D001692:Biological Transport; D002247:Carbon Isotopes; D002462:Cell Membrane / Q000201:enzymology*; D002855:Chromatography, Thin Layer; D002951:Citrates / Q000378:metabolism; D003065:Coenzyme A / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004579:Electron Transport; D004926:Escherichia coli / Q000378:metabolism*; D005632:Fructose / Q000378:metabolism; D005650:Fumarates / Q000378:metabolism; D005690:Galactose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D006885:Hydroxybutyrates / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D007773:Lactates / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D008293:Malates / Q000378:metabolism; D008353:Mannitol / Q000378:metabolism; D008358:Mannose / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010071:Oxaloacetates / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
chemical_list: D000085:Acetates; D002247:Carbon Isotopes; D002951:Citrates; D005650:Fumarates; D006885:Hydroxybutyrates; D007656:Ketoglutaric Acids; D007773:Lactates; D008293:Malates; D010071:Oxaloacetates; D011773:Pyruvates; D009243:NAD; D005632:Fructose; D008353:Mannitol; D009249:NADP; D013395:Sucrose; D000242:Cyclic AMP; D007770:L-Lactate Dehydrogenase; D013385:Succinate Dehydrogenase; D000251:Adenosine Triphosphatases; D005947:Glucose; D007785:Lactose; D005990:Glycerol; D008358:Mannose; D003065:Coenzyme A; D005690:Galactose