Role of materials released from Escherichia coli cells in the catabolite repression of L-arabinose isomerase induced by γ-irradiation

Inhibition of L-arabinose isomerase synthesizing capacity of Escherichia coli by γ-irradiation was withdrawn when the irradiated cells were separated by centrifugation from the suspending medium and were suspended in a fresh growth medium. Further, there was an inhibition of the induced enzyme synthesis in unirradiated cells when suspended in the supernatant from γ-irradiated cell suspension. These findings suggested that some inhibitory material(s) was released from γ-irradiated cells into the suspending medium. Incubation of γ-irradiated cells suspended in fresh growth medium led to an exponential decrease in the enzyme synthesizing capacity, which was not caused by release of any inhibitory material. Cyclic AMP could reverse the inhibition of the enzyme synthesizing capacity in unirradiated cells caused by their suspension in the supernatant from γ-irradiated cell suspension immediately following irradiation suggesting that catabolite repression is the cause of the inhibition. Incubation of γ-irradiated cell suspension released the L-arabinose isomerase-synthesizing system from the catabolite repression. (author). 9 refs., 4 figs