Concept

Nicotinamide adenine dinucleotide phosphate

Summary
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source'). NADPH is the reduced form of NADP, the oxidized form. NADP is used by all forms of cellular life. 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 extra phosphate is added by NAD+ kinase and removed by NADP+ phosphatase. In general, NADP+ is synthesized before NADPH is. Such a reaction usually starts with NAD+ from either the de-novo or the salvage pathway, with NAD+ kinase adding the extra phosphate group. ADP-ribosyl cyclase allows for synthesis from nicotinamide in the salvage pathway, and NADP+ phosphatase can convert NADPH back to NADH to maintain a balance. Some forms of the NAD+ kinase, notably the one in mitochondria, can also accept NADH to turn it directly into NADPH. The prokaryotic pathway is less well understood, but with all the similar proteins the process should work in a similar way. NADPH is produced from NADP+. The major source of NADPH in animals and other non-photosynthetic organisms is the pentose phosphate pathway, by glucose-6-phosphate dehydrogenase (G6PDH) in the first step. The pentose phosphate pathway also produces pentose, another important part of NAD(P)H, from glucose. Some bacteria also use G6PDH for the Entner–Doudoroff pathway, but NADPH production remains the same. Ferredoxin-NADP reductase, present in all domains of life, is a major source of NADPH in photosynthetic organisms including plants and cyanobacteria. It appears in the last step of the electron chain of the light reactions of photosynthesis. It is used as reducing power for the biosynthetic reactions in the Calvin cycle to assimilate carbon dioxide and help turn the carbon dioxide into glucose.
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Related concepts (39)
Pentose phosphate pathway
The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt and the HMP Shunt) is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. While the pentose phosphate pathway does involve oxidation of glucose, its primary role is anabolic rather than catabolic. The pathway is especially important in red blood cells (erythrocytes).
Nicotinamide adenine dinucleotide phosphate
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source'). NADPH is the reduced form of NADP, the oxidized form. NADP is used by all forms of cellular life. 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.
Calvin cycle
The Calvin cycle, light-independent reactions, bio synthetic phase, dark reactions, or photosynthetic carbon reduction (PCR) cycle of photosynthesis is a series of chemical reactions that convert carbon dioxide and hydrogen-carrier compounds into glucose. The Calvin cycle is present in all photosynthetic eukaryotes and also many photosynthetic bacteria. In plants, these reactions occur in the stroma, the fluid-filled region of a chloroplast outside the thylakoid membranes.
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