Glucose catabolism Subject

Cataboirte repression Inhibition of enzyme synthesis by increased concentrations of certain metabolic products. Enzymes subject to Cr. are formed in reponse to metabolic events (utilization of new nutrients by catabolic enzymes, synthesis of secondary products in certain developmental phases of microorganisms). C. r. is probably present in all organisms, although the molecular mechanisms are diverse. Examples of C.r. are glucose repression of catabolic enzymes in . coU and the enzymes of secondary metabolism in microorganisms, e.g. those for the s thesis of penicillin, actinomycin and riboflavin. 

The report that cAMP relieves glucose repression of iV-acetylkanamycin amidohydrolase in Streptomyces kanamyceticus, a prokaryote ( ), indicates that the repression mechanism resembles that of different catabolic enzymes in bacteria, which proceed via the inhibition of adenylate cyclase, the enzyme that converts ATP to cAMP (D 10.4). As a consequence the concentration of cAMP decreases and the transcription by RNA polymerase of operons subjected to cAMP control is inhibited (catabolite repression). In eucaryotes, however, catabolite repression could not be demonstrated. In Penicillium cyclopium for instance, glucose suppression of benzodiazepine alkaloid biosynthesis cannot be overcome by administration of cAMP or cAMP derivatives. 

---