The low energy form NAD⁺ shown at left is raised to the high energy form NADH. The change in the form of the active nicotinamide group in NADH is indicated above. It accepts two electrons and a hydrogen in reaching the high energy state. The NAD⁺ is used in redox reactions in the cell and acts as a reducing agent. NADH contributes to oxidation in cell processes like glycolysis to help with the oxidation of glucose.

NAD⁺ is mostly used in catabolic pathways, such as glycolysis, that break down energy molecules to produce ATP. The ratio of NAD⁺ to NADH is kept very high in the cell, keeping it readily available to act as an oxidizing agent.

NADH is used in the electron transport chain to provide energetic electrons.

Nicotinamide adenine dinucleotide phosphate or NADPH is a reduced coenzyme that plays a key role in the synthesis of carbohydrates in photosynthetic organisms. It is the reduced form of NADP⁺ and as such is a high energy molecule that helps drive the Calvin cycle. NADPH is formed during photosynthesis with the use of light energy in the electron transport chain of chloroplasts. It then represents an energy currency that can be used in the Calvin cycle and subsequent reactions to produce carbohydrates.

NADPH is the reduced form of NADP⁺. NADP⁺ differs from NAD⁺ by the presence of an additional phosphate group. NADP⁺ can be produced from NAD⁺ by means of the enzyme NAD⁺-kinase and then further reduced to NADPH in the pentose phosphate pathway.

While NAD⁺ is usually associated with the catabolic side of metabolism and NADP⁺ with the anabolic side, there are situations where one needs to be converted to the other.

NAD⁺ - kinase is an enzyme that converts nicotinamide adenine dinucleotide (NAD⁺) into NADP⁺ through phosphorylating the NAD⁺ coenzyme. NADP⁺ is an essential coenzyme that is reduced to NADPH primarily by the pentose phosphate pathway to provide reducing power in biosynthetic processes such as fatty acid biosynthesis and nucleotide synthesis.