Pyridine nucleotide cycle of Salmonella typhimurium: regulation of nicotinic acid phosphoribosyltransferase and nicotinamide deamidase

Abstract

Nicotinic acid phosphoribosyl transferase (NAPRTase) and nicotinamide deamidase activities from S. typhimurium were examined regarding their regulation by either feedback inhibition or repression mechanisms. Neither enzyme appears to be subject to feedback inhibition. Nicotinamide deamidase does not appear to be under repression control. NAPRTase is repressed when cells are grown in minimal medium supplemented with various intermediates of the pyridine nucleotide cycle. The concentration of exogenously supplied pyridine nucleotide necessary to effect repression of NAPRTase was that concentration which will result in a nadA mutant generation time of less than 60 min. NAD is the actual corepressor molecule. The analogs 6-aminonicotinic acid and 6-aminonicotinamide were also capable of repressing NAPRTase, but only when an intact pyridine nucleotide cycle permitted conversion to 6-aminonicotinamide adenine dinucleotide. The role of a repressible NAPRTase is discussed in relation to the overall functioning of the pyridine nucleotide cycle.