Range: ±3.6 sec^-1
||Bacteria Escherichia coli
||Smirnova I, Kasho V, Sugihara J, Kaback HR. Opening the periplasmic cavity in lactose permease is the limiting step for sugar binding. Proc Natl Acad Sci U S A. 2011 Sep 13 108(37):15147-51. doi: 10.1073/pnas.1112157108. p.15151 left column bottom paragraphPubMed ID21896727
||Abstract: "In this study, rates of substrate binding were measured by stopped-flow with purified LacY either in detergent or in reconstituted proteoliposomes. Binding rates are compared with rates of sugar-induced opening of the periplasmic pathway obtained by using a recently developed method based on unquenching of Trp fluorescence."
||P.15151 left column bottom paragraph: "A turnover number of 16–20 s^-1 has been estimated for active lactose transport, as measured with WT LacY in RSO [right-side-out] membrane vesicles, as well as inserted into proteoliposomes (ref 16). Very much the same rate is observed here for sugar binding to WT LacY in proteoliposomes (21 ± 3.6 s^-1). Therefore, the opening of the periplasmic gate could be a rate-limiting step in the overall transport process catalyzed by WT LacY."