NADH and NAD+ are a REDOX pair in cells; NADH is the reduced form of the coenzyme NAD+, and NAD+ is its oxidized form. In REDOX reactions, NADH acts as a donor of hydrogen and electron, and NAD+ acts as a acceptor of hydrogen and electron, participating in physiological processes such as respiration, photosynthesis, and alcohol metabolism. As coenzymes in many REDOX reactions in organisms, they participate in life activities and transform each other.