Summary of nucleotide structures and metabolic pathways of interconversion. Color coding: dark blue, ADPR core structure; green, nicotinamide; blue, nicotinic acid; red, 2′-phosphate. In living cells, ADPR and ADPRP are generated from pyridine dinucleotide precursors by the multifunctional enzyme CD38, and degraded into AMP(P) and ribose-5-phosphate by NUDT9. NUDT9 substrates are also activators of TRPM2.