Kcat for lactose permease in cells and vesicles

Range Table - link
Organism Bacteria Escherichia coli
Reference Dornmair K, Overath P, Jähnig F. Fast measurement of galactoside transport by lactose permease. J Biol Chem. 1989 Jan 5 264(1):342-6.PubMed ID2642475
Primary Source 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):497-508.PubMed ID6363073
Method Lactose permease of Escherichia coli was reconstituted into vesicles of dimyristoylphosphatidylcholine (DMPC), and the rate of galactoside counterflow was measured in the millisecond time range: The problem of measuring true initial rates in vesicles is of general relevance, because recently (as of 1989) a number of transport proteins has been isolated and reconstituted into lipid vesicles. The idea was to measure transport in vesicles faster than done conventionally and thus to compensate for their small size. Researchers, therefore, employed a rapid filtration technique which permitted them to observe galactoside transport in the time range of tens of milliseconds, i.e. 2 or 3 orders of magnitude faster than with conventional filtration techniques. Furthermore, they measured transport in the so called counterflow mode by detecting the influx of a labeled substrate into vesicles loaded with another, unlabeled substrate. The imported substrate is transiently accumulated in the vesicles, because the export route is occupied by the other substrate. This means that influx occurs over an extended period of time with the true initial rate.
Comments In all cases, the internal melibiose concentration was 15 mM, pH 7.6, and the temperature was 20 °C. Data from first 4 samples in table link from primary source. See BNID 103159,104098,104176
Entered by Uri M
ID 105064