3-Acetylpyridine adenine dinucleotide (APAD) is a synthetic analog of nicotinamide adenine dinucleotide (NAD⁺), used primarily in biochemical research rather than natural biological systems. It functions as a coenzyme in redox reactions, facilitating electron transfer in dehydrogenase enzyme assays, such as those for alcohol dehydrogenase and lactate dehydrogenase. Its distinct absorbance properties (reduced form at 363 nm) make it ideal for spectrophotometric monitoring without interference from natural NAD/NADH. Commonly employed in studies of metabolic pathways like glycolysis and the citric acid cycle in vitro, as well as in research on NAD-dependent enzymes including sirtuins and poly(ADP-ribose) polymerases related to DNA repair and aging. Widely utilized in diagnostic kits for measuring enzyme activity in clinical and industrial applications.