Pyridine nucleotide cycle of Salmonella typhimurium: isolation and characterization of pncA, pncB, and pncC mutants and utilization of exogenous nicotinamide adenine dinucleotide
- 1 March 1979
- journal article
- research article
- Published by American Society for Microbiology in Journal of Bacteriology
- Vol. 137 (3), 1165-1175
- https://doi.org/10.1128/jb.137.3.1165-1175.1979
Abstract
Mutants of S. typhimurium LT-2 deficient in nicotinamidase activity (pncA) or nicotinic acid phosphoribosyltransferase activity (pncB) were isolated as resistant to analogs of nicotinic acid and nicotinamide. Information obtained from interrupted mating experiments placed the pncA gene at 27 units and the pncB gene at 25 units on the S. typhimurium LT-2 linkage map. A major difference in the location of the pncA gene was found between the S. typhimurium and Escherichia coli linkage maps. The pncA gene is located in a region in which there is a major inversion of the gene order in S. typhimurium as compared to that in E. coli. Growth experiments using double mutants blocked in the de novo pathway to NAD (nad) and in the pyridine nucleotide cycle (pnc) at the pncA or pncB locus, or both, provided evidence for the existence of an alternate recycling pathway in this organism. Mutants lacking this alternate cycle, pncC, were isolated and mapped via cotransduction at 0 units. Utilization of exogenous NAD was examined through the use of [14C]carbonyl-labeled NAD and [14C]adenine-labeled NAD. The results of these experiments suggest that NAD is degraded to NMN at the cell surface. A portion of this extracellular NMN is then transported across the cell membrane by NMN glycohydrolase and degraded to nicotinamide in the process. The remaining NMN accumulates extracellularly and will support the growth of nadA pncB mutants which cannot utilize the nicotinamide resulting from the major pathway of NAD degradation. A model is presented for the utilization of exogenous NAD by S. typhimurium LT-2.This publication has 30 references indexed in Scilit:
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