| Abstrakt: |
Wild-type Escherichia colistrains (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, C14-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. |
