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Mechanism of lactose—proton cotransport in Escherichia coli
Author(s) -
Lancaster Jack R.
Publication year - 1982
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(82)81296-9
Subject(s) - cotransporter , electrochemical gradient , proton , chemistry , symporter , lactose , dimer , substrate (aquarium) , biophysics , escherichia coli , lactose permease , transporter , chemiosmosis , transmembrane protein , stereochemistry , binding site , biochemistry , membrane , enzyme , biology , physics , sodium , ecology , organic chemistry , quantum mechanics , gene , atp synthase , receptor
Rigorous kinetic derivations are presented for the Site Exposure mechanism of lactose—proton cotransport in E. coli [J. Theor. Biol. (1978) 75, 35–50]. Proton translocation inwards is solely associated with the external exposure of the galactoside binding site. A symmetric dimer configuration of the transporter is proposed, resulting in two forms corresponding to the cis and the trans orientation of the binding sites. The cis to trans orientation is inherently unfavorable, induced only by transmembrane substrate gradients. Recently reported extensive kinetic data are straightforwardly predicted by this mechanism, including the complicated effects on the apparent affinity and maximal velocity of uptake exhibited by changes in the magnitude of the proton electrochemical gradient.