Inducible System for the Utilization of β-Glucosides in Escherichia coli I. Active Transport and Utilization of β-Glucosides

Abstract

Wild-type Escherichia coli strains (β- gl − ) do not split β-glucosides, but inducible mutants (β- gl + ) can be isolated which do so. This inducible system consists of a β-glucoside permease and an aryl β-glucoside splitting enzyme. Both can be induced by aryl and alkyl β-glucosides. In β- gl − and noninduced β- gl + cells, C 14 -labeled thioethyl β-glucoside (TEG) is taken up by a constitutive permease, apparently identical with a glucose permease (GP). This permease has a high affinity for α-methyl glucoside and a low affinity for aryl β-glucosides. No accumulation of TEG occurs in a β- gl − strain lacking glucose permease (GP − ). In induced β- gl + strains, there appears a second β-glucoside permease with low affinity for α-methyl glucoside and high affinity for aryl β-glucosides. Autoradiography shows that TEG is accumulated by the β-glucoside permease and glucose permease in two different forms (one being identical with TEG, the other probably phosphorylated TEG). In GP + β- gl + strains with high GP activity, alkyl β-glucosides induce the enzyme and the β-glucoside permease after a prolonged induction lag, and they competitively inhibit the induction by aryl β-glucosides. The induction lag and competition do not exist in GP − β- gl + strains. It is assumed that phosphorylated alkyl and thioalkyl β-glucosides inhibit the induction, and that this inhibition is responsible for the induction lag.