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Nicotinamide riboside kinase (NRK) is an enzyme involved in the metabolism of nicotinamide adenine dinucleotide (NAD+). This enzyme catalyzes the phosphorylation of nicotinamide riboside (NR) to form nicotinamide mononucleotide (NMN). It defines the NR salvage pathway of NAD+ biosynthesis in addition to the pathways through nicotinic acid mononucleotide (NaMN). This enzyme can also phosphorylate the anticancer drug tiazofurin, which is an analog of nicotinamide riboside.