title: Mechanism of lactose-proton cotransport in Escherichia coli. Kinetic results in terms of the site exposure model.
abstract: 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.
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D007785:Lactose / Q000378:metabolism*; D008433:Mathematics; D008954:Models, Biological; D011522:Protons
chemical_list: D011522:Protons; D007785:Lactose