NAD+ Is Not a Peptide
NAD+ (nicotinamide adenine dinucleotide) is definitively not a peptide—it is a pyridine nucleotide coenzyme composed of two nucleotides joined by phosphate groups, one containing adenine and the other containing nicotinamide. 1
Chemical Structure and Classification
NAD+ consists of two nucleotides linked through their phosphate groups, fundamentally different from peptides which are chains of amino acids connected by peptide bonds 2
NAD+ is classified as a pyridine nucleotide, functioning as an electron-shuttling agent and cofactor in enzymatic reduction-oxidation (redox) reactions 1
The molecule exists in oxidized (NAD+) and reduced (NADH) forms, both serving as essential coupled redox metabolites in cellular metabolism 3
Biological Function
NAD+ acts as a coenzyme involved in over 400 enzymatic reactions in the body, playing central roles in energy metabolism, DNA repair, gene expression, and stress responses 2, 4
In neurons and other cells, NADH serves as the principal electron donor in the respiratory chain, being oxidized to NAD+ at complex I to drive mitochondrial oxidative phosphorylation 1
NAD+ also functions as an essential cofactor for non-redox enzymes including sirtuins, CD38, and poly(ADP-ribose) polymerases, which consume NAD+ as a substrate for their catalytic activity 4, 3
Clinical Relevance of the Distinction
Understanding that NAD+ is a nucleotide coenzyme rather than a peptide is critical for appropriate supplementation strategies, as dietary recommendations focus on niacin precursors (16 mg/day for adult males, 14 mg/day for adult females) rather than peptide-based therapies 2
The molecular structure determines absorption and metabolism pathways: NAD+ precursors like nicotinamide, nicotinamide riboside, and nicotinamide mononucleotide are used for supplementation because they can be converted to NAD+ through established biosynthetic pathways 5, 6