General Background Nicotinamide adenine dinucleotide (NAD) and its phosphorylated derivative, nicotinamide adenine dinucleotidephosphate (NADP) are two of the most important coenzymes in redox reactions in the cell. Generally, NAD is involved in catabolic reactions, while NADP is involved in anabolic reactions. Due to the positive charge on the nitrogen atom in the nicotinamide ring, the oxidized forms of these compounds are often depicted as NAD+ and NADP+, respectively . Most oxidative reactions in cells are accomplished by the removal of hydrogen atoms. In reactions where NAD or NADP participate, two hydrogen atoms are typically removed from the substrate. During the reduction of NAD+ (or NADP+) the molecule acquires two electrons and one proton, while the second proton is released into the medium. Thus a typical reaction involving NAD is in the form: NAD+ + 2H -> NADH + H+ NAD+ also has myriad nonredox roles in the cell. It is a substrate in posttranslational covalent modifications of key proteins, such as mono- and poly-ADP ribosylation reactions. NAD+ homeostasis is related to the production of reactive oxygen species responsible for irreversible cellular damage in a number of diseases . It also plays a role in longevity and transcriptional silencing through the regulation of : ENSG00000096717-MONOMER (SIRT1), the human homolog of the S. cerevisiae SIR2 protein known to be involved in cell aging and response to DNA damage . NAD+ is synthesized via two major pathways in humans; the : NADSYN-PWY and : NAD-BIOSYNTHESIS-III pathways. About this Pathway This pathway represents an NAD+ salvage pathway for the synthesis of : NAD. The key enzymes, : CPLX66-383 and : CPLX66-380 recycle : NIACINAMIDE to generate : NAD. The enzyme : CPLX66-383 catalyzes the conversion of : NIACINAMIDE to : NICOTINAMIDE_NUCLEOTIDE . The enzyme localizes to both the cytosol and nucleus. The : NICOTINAMIDE_NUCLEOTIDE is converted to : NAD by : CPLX66-380 . The nuclear NAD+ salvage pathway regulates the functions of NAD+ dependent nuclear enzymes such as : ENSG00000096717-MONOMER "SIRT1"

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