NADP+

Nicotinamide adenine dinucleotide phosphate (NADP+) is a coenzyme found in all living cells. It is a dinucleotide, which means it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine base and the other contains nicotinamide. NADP+ is the oxidized form of NADPH, which is a critical reducing agent involved in the antioxidant defense and reductive biosynthesis.

Structure

NADP+ differs from NAD+ by the presence of an additional phosphate group on the 2' position of the ribose ring that carries the adenine moiety. This structural difference is critical in enabling enzymes to distinguish between NADH and NADPH, which are involved in different metabolic pathways.

Function

NADP+ functions primarily as an electron carrier, cycling between the oxidized form (NADP+) and the reduced form (NADPH). This cycling is crucial in various biochemical pathways, including:

• Photosynthesis, where NADPH is generated during the light-dependent reactions to be used in the Calvin cycle.
• Fatty acid synthesis and cholesterol synthesis, where NADPH provides the reducing equivalents.
• The pentose phosphate pathway, which generates NADPH and ribose-5-phosphate, the latter being a precursor for the synthesis of nucleotides.

NADP+ is also involved in the detoxification of reactive oxygen species in the cytosol and mitochondria, with NADPH being a vital component of the glutathione and thioredoxin systems that reduce peroxides.

Biosynthesis

NADP+ is synthesized from NAD+ by the action of the enzyme NAD+ kinase, which transfers a phosphate group to the 2' position of the adenosine ribose in NAD+. This reaction is ATP-dependent.

Clinical Significance

Alterations in NADP+/NADPH levels have been implicated in various diseases, including diabetes mellitus, cancer, and neurodegenerative diseases. NADPH is essential for the regeneration of glutathione, one of the main antioxidants in the body, and a deficiency in NADPH can lead to increased oxidative stress and cell damage.

See Also

• Oxidative phosphorylation
• Redox
• Coenzymes
• Metabolism