Fig. 1.

a Structure of nicotinamide adenine dinucleotide (NAD⁺). This molecule is formed by adenosine monophosphate (AMP) linking to nicotinamide mononucleotide (NMN). AMP is formed by adenosine (in green), ribose ring (in blue) whose hydroxyl (marked in red) can be phosphorylated resulting in NADP+, and phosphate group (in orange). NMN is formed by a ribose ring, phosphate group, and nicotinamide (NAM) (in pink) that is responsible for redox NAD⁺ functions, thus, the atom carbon (marked in red) is capable of accepting a hydride anion (H+, 2e-) leading to the reduced form NADH. In addition to the classical redox functions, NAD⁺ acts as a substrate of multiples enzymes donating the group adenosine diphosphate ribose (ADP-ribose) and releasing nicotinamide as the catabolic reaction product. b Structure of the different states of NAD⁺. NAD⁺ can be phosphorylated to NADP⁺ by NADK enzyme. Thus, NAD⁺ and NADP⁺ can be reduced to NADH or NADPH, respectively. NADH nicotinamide adenine dinucleotide, NAD⁺ nicotinamide adenine dinucleotide, NADP⁺ nicotinamide adenine dinucleotide phosphate, NADPH reduced nicotinamide adenine dinucleotide phosphate