Differentiation between binding and transport of dansylgalactosides in Escherichia coli

The results presented in this paper confirm and extend previous observations which indicate that fluorescent dansylgalactsodes bind to the beta-galactoside carrier protein but do not penetrate the cytoplasmic membrane. The conclusion is supported by the following observations. (a) Although 2'-(N-dansyl)aminoethyl-beta-D-thiogalactopyranoside and 2'-(N-dansyl)aminoethyl-beta-D-galactopyranoside are competitive inhibitors of lactose transport in intact cells of Escherichia coli and induce the in vitro synthesis of beta-galactosidase, they do not induce beta-galactosidase in vivo. (b) p-Chloromercuribenzenesulfonate does not cause efflux of lactose from the intravesicular pool, but causes rapid reversal of D-lactate-induced dansylgalactoside fluorescence. (c) Dansylgalactosides inhibit dilution-induced, carrier-mediated lactose efflux.