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Induction and Repression of L-Arabinose Isomerase in Salmonella typhimurium

Department of Biochemistry and Biophysics, College of Medical Sciences, Banaras Hindu University, Varanasi-5, U.P., India

ABSTRACT

As with other inducible enzymes, the induced synthesis of L-arabinose isomerase (L-arabinose ketol isomerase, EC 5.3.1.4) in Salmonella typhimurium is subject to catabolite repression. Of the three catabolite repressors tested, glucose produces maximum repression. Analogues of catabolite repressors like 2-deoxy-D-glucose and D-fucose also inhibit the synthesis of the enzyme. The catabolite repression is completely reversed in the presence of 1.5 x 10^–3M cyclic 3',5'-adenosine monophosphate (AMP). The maximum repression is produced in glucose-grown cells in glucose-containing induction medium. Cyclic 3',5-AMP reverses this repression provided that the cells are treated with ethylenediaminetetraacetic acid (EDTA). In normal cells, cyclic 3',5'-AMP has no effect on the induction but in EDTA-treated cells the cyclic nucleotide enhances synthesis of the enzyme. The inhibition produced by D-fucose cannot be reversed by cyclic 3',5'-AMP. D-Fucose competes with the inducer L-arabinose in some step(s) involved in the process of induction.