Effect of lithium ion on melibiose transport in Escherichia coli.
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.
D001693:Biological Transport, Active / Q000187:drug effects; D004187:Disaccharides / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology*; D008756:Methylgalactosides / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D013862:Thiogalactosides / Q000378:metabolism
D004187:Disaccharides; D008756:Methylgalactosides; D013862:Thiogalactosides; C009468:thiomethylgalactoside; D008094:Lithium; D012964:Sodium