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  • Title: Effect of lithium ion on melibiose transport in Escherichia coli.
    Author: Tsuchiya T, Lopilato J, Wilson TH.
    Journal: J Membr Biol; 1978 Jul 21; 42(1):45-59. PubMed ID: 353286.
    Abstract:
    Both Li+ and Na+ stimulated the uptake of thiomethylgalactoside by the melibiose transport system of Escherichia coli. On the other hand, Li+ inhibited the growht of cells on melibiose as a sole source of carbon. This inhibition was specific for melibiose, and Li+ had no effect on growth of cells on glucose, galactose, lactose, or glycerol. The effect of the cation on melibiose transport was investigated in a mutant which cannot utilize glucose. After entry into this cell, melibiose is cleaved into glucose and galactose by alpha-galactosidase, and the resulting glucose is excreted. Since the entry step was found to be rate-limiting, glucose production could be taken as a measure of melibose transport. Li+ inhibited the transport of melibiose, but not the induction of the melibiose operon nor the activity of alpha-galactosidase. Li+ was found to inhibit the entry of p-nitrophenyl-alpha-D-galactoside, but not p-nitrophenyl-beta-D-galactoside entry. Thus, the cation specificity for the melibiose membrane carrier varies different transport substrates.
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