Many HDACs exist in mammalian cells. Class III HDACs, also known as sirtuins, are nicotinamide adenine dinucleotide (NAD)-dependent deacetylases (98). NAD is a coenzyme carrying electrons between redox reactions in its reduced form NADH. More than 200 metabolic enzymes use NAD+/NADH as a cofactor, most functioning in catabolism. For example, starting with one glucose molecule, two NAD+ molecules are reduced to NADH in glycolysis, at the step catalyzed by glyceraldehyde 3-phosphate dehydrogenase. The highly related NADP+/NADPH performs the same role for enzyme catalyzed anabolic reactions, for example in the de novo synthesis of palmitate by FASN.
