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

<jats:p> Wild-type <jats:italic>Escherichia coli</jats:italic> strains (β- <jats:italic>gl</jats:italic> <jats:sup>−</jats:sup> ) do not split β-glucosides, but inducible mutants (β- <jats:italic>gl</jats:italic> <jats:sup>+</jats:sup> ) 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- <jats:italic>gl</jats:italic> <jats:sup>−</jats:sup> and noninduced β- <jats:italic>gl</jats:italic> <jats:sup>+</jats:sup> cells, C <jats:sup>14</jats:sup> -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- <jats:italic>gl</jats:italic> <jats:sup>−</jats:sup> strain lacking glucose permease (GP <jats:sup>−</jats:sup> ). In induced β- <jats:italic>gl</jats:italic> <jats:sup>+</jats:sup> 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 <jats:sup>+</jats:sup> β- <jats:italic>gl</jats:italic> <jats:sup>+</jats:sup> 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 <jats:sup>−</jats:sup> β- <jats:italic>gl</jats:italic> <jats:sup>+</jats:sup> strains. It is assumed that phosphorylated alkyl and thioalkyl β-glucosides inhibit the induction, and that this inhibition is responsible for the induction lag. </jats:p>