enzymeNAD

enzymeNAD is a term used in certain educational resources and some databases to denote enzymes that require nicotinamide adenine dinucleotide (NAD+) or its phosphorylated form NADP+ as a cofactor, or that catalyze reactions in which NAD+/NADH serves as a key redox couple. In common biochemical usage, these are called NAD-dependent or NADP-dependent oxidoreductases and encompass a broad set of dehydrogenases and related enzymes.

Mechanism: Most NAD-dependent dehydrogenases catalyze hydride transfer from the substrate to the nicotinamide ring of the dinucleotide, converting NAD+ to NADH or NADP+ to NADPH. Binding often involves conserved nucleotide-binding motifs, such as the Rossmann fold, which facilitates dinucleotide interaction and catalysis.

Biological role: NAD-dependent enzymes are central to energy metabolism and redox regulation. In glycolysis, glyceraldehyde-3-phosphate dehydrogenase uses NAD+. In the citric acid cycle, malate dehydrogenase uses NAD+. In anaerobic fermentation, lactate dehydrogenase regenerates NAD+. NAD(P)H also serves as a reducing power in biosynthetic pathways and in cellular defense against oxidative stress.

Structure and regulation: Many enzymes in this class share structural features, including Rossmann-like dinucleotide-binding domains. Activity is influenced by cellular NAD+/NADH ratios, allosteric effectors, and gene expression in response to metabolic state or stress.

Applications: NAD-dependent enzymes are widely used in biotechnology and biosensing. They enable cofactor recycling schemes for sustainable synthesis and are used as targets in metabolic engineering to optimize redox balance.