Enzymatic characterization of nad pyrophosehatase, genetic regulation of pnue, and the function of pnue and nad pyrophosephatase in the salmonella typhimurium nad recycling pathway

The gene pnuE in Salmonella typhimurium encodes nicotinamide adenine dinucleotide (NAD) pyrophosphatase, whose active site is contained in the periplasm of the bacterium. This periplasmic NAD pyrophosphatase catalyzes the pyrophosphorolysis, or breakdown, of extracellular NAD to nicotinamide mononucleotide (NMN) and adenosine monophosphate (AMP). Evidence presented in this research paper suggests that the pnuE gene is expressed constitutively. NAD pyrophosphotase may function as a general phosphotase; however, NAD pyrophosphatase does not appear to have any NADP pyrophosphatase activity based on data obtained from assay reaction mixtures that contained NADP and cell extracts. NAD pyrophosphatase may function also as a UDPsugar pyrophosphatase, a possibility supported by the constitutive expression of gene pnuE. NAD pyrophosphatase contributes very little, if at all, to NAD breakdown, or pyrophosphorolysis, inside the cell. The extracellular pyrophosphorolysis of NAD may be useful to the pathogenesis of S. typhimurium.