Nicotinamide riboside kinase 1 is an enzyme that in humans is encoded by the NMRK1 gene. As both a nicotinate riboside kinase (), and a ribosylnicotinamide kinase (), this enzyme helps perform a step in the process of converting certain forms of niacin/Vitamin B3 into active coenzymes like NAD+. In humans, nicotinamide riboside kinase 1 is expressed in most tissues of the body, compared to the other isozyme, nicotinamide riboside kinase 2, which is predominantly found in muscles.
Function The enzyme can act as both a ribosylnicotinamide kinase (), catalyzing the reaction:
beta-nicotinamide D-ribonucleotide + diphosphate = 5-phospho-alpha-D-ribose 1-diphosphate + nicotinamide + H(+)
and a nicotinate riboside kinases () and catalyze:
ATP + β-D-ribosylnicotinate = ADP + nicotinate β-D-ribonucleotide
In particular, it converts nicotinamide riboside into nicotinamide mononucleotide (NMN) and nicotinic acid riboside into nicotinic acid mononucleotide (NaMN). This reaction is part of one of the pathways of producing NAD+, but NMN can also be directly produced from nicotinamide through the action of the enzyme nicotinamide phosphoribosyltransferase (see for more details).
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