Turnover number for lactose permease (LacY)

Value 21 sec^-1 Range: ±3.6 sec^-1
Organism Bacteria Escherichia coli
Reference 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
Method 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."
Comments 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."
Entered by Uri M
ID 112482