In 1958, Jack Preiss and Philip Handler published a scientific paper describing how NAD+ was made from niacin in three steps.(1) This pathway was later named the Preiss-Handler pathway after the co-discoverers. It describes the enzyme steps needed to convert niacin into the NAD+ molecule.
The salvage pathway is used to produce NAD+ from nicotinamide molecules. Whether the source of the nicotinamide is vitamin B3 (as niacinamide), newer nicotinamides (e.g., nicotinamide riboside [NR], nicotinamide mononucleotide [NMN]), or molecules in food that get broken down during digestion into nicotinamide, the salvage pathway turns them into NAD+ in our tissues.
Most organisms have several alternatives for producing the NAD+ molecule. In humans, there are three major NAD+ biosynthesis pathways: the De Novo Pathway, starting from the essential amino acid L-tryptophan; the Preiss-Handler pathway, using niacin (nicotinic acid); and the Salvage Pathway from niacinamide (nicotinamide). In this article, we’ll be covering the De Novo Pathway.
