title: Transport of L-Lactate, D-Lactate, and glycolate by the LldP and GlcA membrane carriers of Escherichia coli.
abstract: To examine the substrate specificity of the membrane transport carriers LldP (L-lactate permease) and GlcA (glycolate permease) of Escherichia coli, a mutant strain lacking their structural genes and blocked in the metabolism of the tested substrates was constructed and transformed with a plasmid bearing either the lldP or the glcA gene. Each transformant acquired the ability to accumulate L-lactate, D-lactate, and glycolate against a high concentration gradient. Substrate accumulation was inhibited by carbonyl cyanide m-chlorophenylhydrazone, a hydrophobic proton conductor that dissipates proton motive force. Competition of (14)C-L-lactate transport by nonradioactive L-lactate, D-lactate, and glycolate in LldP synthesizing cells and competition of (14)C-glycolate transport by the same three substrates in GlcA synthesizing cells showed that both carriers effectively transported all three substrates with a K(i) value ranging from 10 to 20 microM. D-Lactate does not appear to have a permease of its own. Utilization of the compound depends mainly on LldP.
authors.affiliation: Department of Biochemistry, Faculty of Pharmacy, University of Barcelona, Avenida Diagonal 643, Barcelona, 08028, Spain.
authors.forename: María Felisa
authors.initials: MF
authors.lastname: Núñez
authors.forename: Ohsuk
authors.initials: O
authors.lastname: Kwon
authors.forename: T Hastings
authors.initials: TH
authors.lastname: Wilson
authors.forename: Juan
authors.initials: J
authors.lastname: Aguilar
authors.forename: Laura
authors.initials: L
authors.lastname: Baldoma
authors.forename: Edmund C C
authors.initials: EC
authors.lastname: Lin
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D006016:Glycolates / Q000378:metabolism* / Q000493:pharmacokinetics; D019344:Lactic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D011522:Protons; D013237:Stereoisomerism; D013379:Substrate Specificity; D014169:Transformation, Bacterial / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins; D006016:Glycolates; C083722:LldP protein, E coli; D026901:Membrane Transport Proteins; D011522:Protons; C031149:glycolic acid; D019344:Lactic Acid; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D019342:Acetic Acid