Overview:

Nicotinamide adenine dinucleotide (NAD) is a coenzyme necessary for the catalytic reaction of certain metabolic enzymes found in all living cells (1). It consists of two nucleosides joined by a pyrophosphate (2). Enzymes catalyze the reversable transfer of a hydride ion (H-) from the substrate molecule to NAD to form the reduced product NADH. The reaction is easily reversible, when NADH reduces another molecule and is re-oxidized to NAD+. Thus, the coenzyme can continuously cycle between the NAD+ and NADH forms without being consumed (3). Laboratory applications of this enzyme include biocatalytic synthesis reactions, and kinetic studies. It can also be used as a cofactor in various diagnostic tests.

References:

1. Pollak N, Dölle C, Ziegler M. The power to reduce: pyridine nucleotides--small molecules with a multitude of functions. Biochem J. 2007 Mar 1;402(2):205-18. doi: 10.1042/BJ20061638. PMID: 17295611; PMCID: PMC1798440.
2. Alfred D. Winer. Crystallization of Nicotinamide Adenine Dinucleotide,Journal of Biological Chemistry,Volume 239, Issue 10,1964,Pages PC3598-PC3600,ISSN 0021-9258. https://doi.org/10.1016/S0021-9258(18)97765-3.
3. Katsyuba E, Romani M, Hofer D, Auwerx J. NAD+ homeostasis in health and disease. Nat Metab. 2020 Jan;2(1):9-31. doi: 10.1038/s42255-019-0161-5. Epub 2020 Jan 20. PMID: 32694684.