Nicotinate mononucleotide

This enzyme [EC 2.4.2.19], also referred to as nicotinate mononucleotide pyrophosphorylase (carboxylating), catalyzes the reversible reaction of pyridine 2,3-dicar-boxylate and 5-phospho-a-o-ribose 1-diphosphate to produce nicotinate D-ribonucleotide, carbon dioxide, and pyrophosphate. 

Nicotinate phosphoribosyltransferase catalyzes the formation of nicotinate mononucleotide (NaMN) and pyrophosphate from 5-phosphoribosyl-a-D-pyrophosphate (PRibPP) and free nicotinic acid. The reaction requires the hydrolysis of ATP to ADP. 

NAD and NADP co factor biosynthesis NadD - nicotinate mononucleotide [B] 27 Cloned from Escherichia coli, enzyme assay 28... 

DMB is converted into a nucleoside to give a-ribazole. This reaction is catalyzed by the P. denitrificans CobU " or S. enterica CobT (Figure 21 y The activation sees the formation of an Ma-glycosidic bond between ribose of /3-nicotinate mononucleotide (NaMN) and DMB with the release of nicotinate. The resulting product, a-ribazole 5 -phosphate is subsequently hydrolyzed by an uncharacterized 5 -phosphatase to give a-ribazole. 

Quinolinatephosphoribosyltransferase(decarboxylating) 2 nicotinate mononucleotide adenylyl-transferase 3 nicotinamide adenine dinucleotide synthetase 4 NAD(P)+ nucleosidase 5 nicotin-amidase 6 nicotinate phosphoribosyltransferase... 

Quinolinate decarboxylation and conversion to nicotinic acid mononucleotide is catalysed by quinolinate phosphoribosyltransferase, a rate-limiting enzyme in the conversion of tryptophan to NAD the reaction requires Mg and is negatively regulated by nicotinamide. Next the transfer of adenylate from ATP by an intermediate of nicotinamide/nicotinate-mononucleotide-adenyl-transferases isoenzymes (NMNAT, see below) yields nicotinic acid adenine... 

Figure 7.3 NAD recycling. Humans have two metabolic pathways that are able to recycle nicotinamide. NAD-consuming enzymes (ARTs, PARPs, sirtuins) break down NAD to nicotinamide and ADP-ribosyl product. Nicotinamide by the enzymatic action of nicotinamide phosphoribosyltransferase (NAMP/PBEF) and nicotinamide/nicotinate-mononucleotide-adenyltransferases isoenzymes (NMATl-3) is then retransformed to NAD. In a second pathway, nicotinamide riboside is phosphorylated by nicotinamide riboside kinase (NRK 1,2) to nicotinamide mononucleotide. Subsequently, nicotinamide mononucleotide is converted to NAD by the catalytic action of NMNATs.

JR Trzebiatowski, JC Escalante-Semerena. Purification and characterization of CobT, the nicotinate-mononucleotide 5,6-dimethylbenzimidazole phosphoribosyl-transferase enzyme from Salmonella typhimurium LT2. J Biol Chem 272 17662-17667, 1997. 

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