Inducible system for the utilization of beta-glucosides in Escherichia coli. I. Active transport and utilization of beta-glucosides

Abstract

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