Transport systems for galactose and galactosides in Escherichia coli: II. Substrate and inducer specificities

Abstract Genetic and biochemical studies have shown Escherichia coli K12 to have four transport systems for galactose and galaetosides: galactose permease, methylgalactoside permease, TMG I and TMG II permeases. Biochemical evidence suggested that they have some substrates and inducers in common. In order to define more clearly the specificities of the individual transport systems, particularly those of the galactose and methylgalaetoside permeases, we examined and compared mutants of E. coli K12, which, by their patterns of accumulation of various sugars, appear to lack one or more of the permeases. From these studies we concluded that the four permeases do show some similarities in the sugars which they transport, and which act as inducers. However, the galactose and methylgalactoside permeases can be distinguished from each other and from the TMG I and TMG II permeases by their substrate and inducer preferences. The only compound found to be transported by the galactose permease was d -galactose. d -Galactose is also the most effective inducer of this transport system. The methylgalactoside permease transported methyl-β- d -galactopyranoside, d -fucose and ethyl-β- d -galactopyranoside, as well as d -galactose. The most effective inducer of this system is d -fucose