Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide and coenzyme present in all living cells. At the biochemical level, NAD+ functions primarily as an electron carrier in cellular respiration, oscillating between its oxidized (NAD+) and reduced (NADH) states to facilitate metabolic redox reactions. In experimental models, NAD+ acts as a required substrate for various enzymatic processes, notably those involving sirtuins (SIRT) and poly (ADP-ribose) polymerases (PARPs). Laboratory research frequently utilizes NAD+ compounds to investigate cellular energy metabolism, enzyme kinetics, and intracellular signaling pathways.