Rate of transport of H+/Lactose transporter

Range 20-50 sec^-1
Organism Bacteria Escherichia coli
Reference Naftalin RJ, Green N, Cunningham P. Lactose permease H+-lactose symporter: mechanical switch or Brownian ratchet? Biophys J. 2007 May 15 92(10):3474-91. p.3475 right column 2nd paragraph & p.3483 left column 4th paragraphPubMed ID17325012
Primary Source [37] Dornmair K, Overath P, Jähnig F. Fast measurement of galactoside transport by lactose permease. J Biol Chem. 1989 Jan 5 264(1):342-6. [38] Wright JK, Overath P. Purification of the lactose:H+ carrier of Escherichia coli and characterization of galactoside binding and transport. Eur J Biochem. 1984 Feb 1 138(3):497-508PubMed ID2642475, 6363073
Comments "Another problem in reconciling H322 with its assigned role in the cyclic process leading to H+-lactose symport is that its proton turnover rate should match the turnover rate of the symporter, i.e., 20–50 Hz (primary sources). Nachliel and Gutman (39,40) have shown that protons diffuse rapidly within the large, water-filled central cavity of LacY, and protonation rates of H322, over a wide pH range, are two orders of magnitude faster than the turnover rate of the symporter in the presence or absence of lactose. This is discordant with a symport model, which requires synchronized mechanical linkages between the various stages of proton-lactose transit and the conformational changes they evoke. It would seem that the rapid rate of Brownian motion within the central cavity militates against such a precise clockwork model." "The relatively slow rate of proton pumping of LacY permease (turnover rate ~20–50 s^-1) (primary sources) is consistent with the low probability of proton escape from the central cavity. However, as seen above, this does not correlate with the microscopic rates of deprotonation of H322 within the central cavity." See BNID 104098,104176,105064
Entered by Uri M
ID 103159