NADP+

Meaning: NADP⁺ is NAD⁺ with an extra phosphate on the ribose of the adenosine half. It accepts a hydride (two electrons and one proton) to form NADPH, which then donates electrons to other molecules. NADPH supplies reducing power for anabolic reactions such as fatty acid and cholesterol synthesis, and for regenerating reduced glutathione. In most cells it is made mainly by the oxidative phase of the pentose phosphate pathway, where glucose-6-phosphate dehydrogenase catalyzes the regulated first step. In plants, NADP⁺ is the final electron acceptor of the light reactions, and the NADPH produced drives the Calvin cycle.

Equation: NADP⁺ + 2e⁻ + H⁺ → NADPH. NADP⁺ is the oxidized carrier and NADPH the reduced carrier (both measured in mol or mol/L), e⁻ is an electron (charge −1.60 × 10⁻¹⁹ C), and H⁺ is a proton.

On the MCAT: Passages on the pentose phosphate pathway ask what happens if glucose-6-phosphate dehydrogenase is impaired. NADPH falls, so reductive biosynthesis and glutathione recycling suffer. Photosynthesis questions ask where NADP⁺ is reduced (light reactions) and where NADPH is consumed (Calvin cycle).

Common confusion: Students treat NADP⁺ as interchangeable with NAD⁺. NAD⁺ is mainly an oxidant in catabolism (glycolysis, citric acid cycle) and its NADH feeds the electron transport chain. NADPH is mainly used in anabolism. Enzymes distinguish the two by the extra phosphate.