NAD+ metaboliset tiet , myös sirtuiinit tässä kartassa. ADP-ribosylaatioreaktiot solussa.

http://mmbr.asm.org/content/70/3/789/F1.expansion.html#ref-339
Tämä on hyvä kartta, joka kannattaa piirtää muistiin. 

Nuclear ADP-Ribosylation Reactions in Mammalian Cells: Where Are We Today and Where Are We Going

 FIG. 1.

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Mammalian NAD⁺ metabolic pathways. The biosynthesis of NAD⁺ occurs through both de novo and salvage pathways (339). In mammalian cells, 90% of free tryptophan is metabolized through the kynurenine pathway, leading to the de novo synthesis of NAD⁺. The three different salvage pathways start either from nicotinamide (Nam), nicotinic acid (Na), or nicotinamide riboside (NR). In mammals, the origin of nicotinic acid is mainly nutritional. Nicotinamide, a product of NAD⁺ hydrolysis, is first converted into nicotinamide mononucleotide (NMN) and then into NAD⁺ by nicotinamide phosphoribosyl transferase (NamPRT) and nicotinamide mononucleotide adenylyl transferases (Na/NMNAT-1, -2, and -3), respectively. Nicotinamide riboside was recently shown to serve as a precursor for NAD⁺ synthesis, connected to the Nam salvage pathway through NMN (36). Nicotinamide riboside is converted to NMN by the ATP-consuming nicotinamide riboside kinases 1 and 2 (NRK-1 and -2) (36). Nicotinic acid can be converted through the Preiss-Handler salvage pathway into nicotinic acid mononucleotide (NaNM) and nicotinate adenine dinucleotide by the concerted actions of nicotinic acid phosphoribosyl transferase (NaPRT) and Na/NMNAT-1, -2, and -3, respectively. Nicotinate adenine dinucleotide is directly transformed into NAD⁺ by the glutamine-hydrolyzing NAD⁺ synthetase (NADS). Na/NMNATs are ATP-consuming enzymes, using either NaMN or NMN as a substrate. Whether both NamPRT and NaPRT are also ATP-consuming enzymes in vivo is not certain. Thus, when the Preiss-Handler salvage pathway is used, the cell invests three or four molecules of ATP from Na to NAD⁺, depending on whether NaPRT is also an ATP-consuming enzyme in vivo. In mammalian cells, under the conditions where NAD⁺ is used as a glycohydrolase substrate, the Nam salvage pathway is required, since there is no nicotinamidase to produce nicotinic acid. Depending on whether NamPRT uses one ATP molecule to convert Nam into NMN, the Nam salvage pathway consumes two or three ATP molecules from Nam to NAD⁺. The de novo pathway is connected to the Preiss-Handler salvage pathway through NaMN. NAD⁺ can be hydrolyzed by various enzymatic activities, such as PARPs, MARTs, SIRTs, and ADP-ribosyl cyclases, which release the Nam moiety from NAD⁺ to produce poly-ADP-ribose, mono-ADP-ribosyl-protein, acetyl-ADP-ribose (O-AADPR), or cyclic-ADP-ribose (cADPR) and nicotinate adenine dinucleotide phosphate (NAADP), respectively. These products are then further metabolized by different hydrolase activities, yielding ADP-ribose (ADPR), which, in turn, can be transformed into 5-phosphribosyl-1-pyrophosphate (PRPP) by the ATP-consuming ADP-ribose pyrophosphatase (ARPP)/ribose phosphate pyrophosphokinase (RPPK) pathway. PRPP is used by the Nam salvage pathway enzymes NamPRT and NaPRT.