RESUMO
The mechanism of catabolite repression caused by sugar transported via the phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) and stipulated by the decrease of the adenylate cyclase activity was studied. It was demonstrated that the sensitivity of the adenylate cyclase and beta-galactosidase synthesis to methyl-L-D-glucoside (MeGlc) or sorbitol is correlated with the content and activity of glucose (EIIGlc) or mannitol enzyme II of the PTS, correspondingly. Under anaerobic conditions the cells become insensitive to catabolic repression caused by MeGlc and the adenylate cyclase activity does not decrease in the presence of the sugar despite the increased rate of MeGlc transport. The adenylate cyclase activity of the mutant with the Tn5 transposone inserted into the ptsG gene does not change in the presence of MeGlc, while the activity of adenylate cyclase and the differential rate of beta-galactosidase synthesis increase in these bacteria. The data obtained confirm the hypothesis on the "catabolite signal" which is generated when the substrate binds to its transporter, i. e. adenylate cyclase reacts to the conformational changes in the transporter being complexed with it. The strength of this complex depends on the affinity of adenylate cyclase for the transporter and on the value of the membrane potential, delta mu H+ A model is proposed, which explains the necessity of factor IIIGlc for EIIGlc binding to adenylate cyclase.
