title: Nicotinate, quinolinate and nicotinamide as precursors in the biosynthesis of nicotinamide-adenine dinucleotide in barley.
abstract: 1. The relative efficiencies of nicotinate, quinolinate and nicotinamide as precursors of NAD(+) were measured in the first leaf of barley seedlings. 2. In small amounts, both [(14)C]nicotinate and [(14)C]quinolinate were quickly and efficiently incorporated into NAD(+) and some evidence is presented suggesting that NAD(+) is formed from each via nicotinic acid mononucleotide and deamido-NAD. 3. [(14)C]Nicotinamide served equally well as a precursor of NAD(+) and although significant amounts of [(14)C]NMN were detected, most of the [(14)C]NAD(+) was derived from nicotinate intermediates formed by deamination of [(14)C]nicotinamide. 4. Radioactive NMN was also a product of the metabolism of [(14)C]nicotinate and [(14)C]quinolinate but most probably it arose from the breakdown of [(14)C]NAD(+). 5. In barley leaves where the concentration of NAD(+) is markedly increased by infection with Erysiphe graminis, the pathways of NAD(+) biosynthesis did not appear to be altered after infection. A comparison of the rates of [(14)C]NAD(+) formation in infected and non-infected leaves indicated that the increase in NAD(+) content was not due to an increased rate of synthesis.
mesh_terms: D001203:Ascomycota; D002247:Carbon Isotopes; D002845:Chromatography; D002523:Edible Grain; D009243:NAD / Q000096:biosynthesis*; D009536:Niacinamide / Q000378:metabolism*; D009539:Nicotinic Acids / Q000378:metabolism*; D010935:Plant Diseases; D010944:Plants / Q000378:metabolism*; D011725:Pyridines / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D009539:Nicotinic Acids; D011725:Pyridines; D009243:NAD; D009536:Niacinamide