Comparative Analysis of Cofactor Binding in NAD⁺- and FAD⁺-Dependent Dehydrogenases: Evolutionary and Kinetic Perspectives

Background: Dehydrogenases constitute a large class of redox enzymes that catalyze the transfer of electrons in metabolic pathways using nicotinamide adenine dinucleotide (NAD⁺) or flavin adenine dinucleotide (FAD⁺) as essential cofactors. While both cofactors serve as electron carriers, they differ in their chemical properties, binding modes, and evolutionary roles across enzyme families. A comprehensive comparison of NAD⁺- and FAD⁺-dependent dehydrogenases offers critical insights into the structural adaptations, kinetic mechanisms, and regulatory strategies that underpin metabolic control and energy homeostasis. Methods and Results: This review systematically examines the structural and functional characteristics of NAD⁺- and FAD⁺-binding dehydrogenases using phylogenetic analyses, crystallographic data, and enzyme kinetics. NAD⁺-dependent enzymes typically exhibit transient cofactor interactions and function as soluble cytosolic catalysts in glycolysis and the TCA cycle. In contrast, FAD⁺-dependent dehydrogenases often contain covalently or tightly bound flavin groups and are associated with membrane-bound or mitochondrial respiratory complexes, reflecting their roles in more sustained redox processes. Comparative kinetic analyses reveal differences in reaction rates, substrate affinities, and catalytic efficiency, often linked to cofactor availability and conformational dynamics. The implications for synthetic biology and metabolic engineering are also addressed, with emphasis on cofactor engineering, enzyme redesign, and pathway optimization for industrial biocatalysis. Conclusion: NAD⁺- and FAD⁺-dependent dehydrogenases represent evolutionarily distinct but functionally convergent enzyme systems. Understanding the structural and kinetic basis of cofactor specificity enriches our knowledge of metabolic evolution and opens new avenues for the rational design of redox enzymes in biomedical and biotechnological applications.