<unk> , abbreviated<unk> +, is a coenzyme found in all living cells. The compound is a<unk> , since it consists of two nucleotides joined through their phosphate groups: with one nucleotide containing an adenosine ring, and the other containing<unk> .
In metabolism,<unk> + is involved in redox reactions, carrying electrons from one reaction to another. The coenzyme is therefore found in two forms in cells:<unk> + is an oxidizing agent – it accepts electrons from other molecules and becomes reduced, this reaction forms<unk> , which can then be used as a reducing agent to donate electrons. These electron transfer reactions are the main function of<unk> +. However, it is also used in other cellular processes, notably as a substrate of enzymes that add or remove chemical groups from proteins, in posttranslational modifications. Due to the importance of these functions, the enzymes involved in<unk> + metabolism are targets for drug discovery.
In organisms,<unk> + can be synthesized from scratch (de novo) from the amino acids tryptophan or aspartic acid. Alternatively, components of the coenzymes are taken up from food as the vitamin called niacin. Similar compounds are released by reactions that break down the structure of<unk> +. These preformed components then pass through a salvage pathway that recycles them back into the active form. Some<unk> + is also converted into<unk>  phosphate <unk> P+); this related coenzyme has similar chemistry to<unk> +, but has different roles in metabolism.
Nicotinamide adenine dinucleotide
Pyridoxal phosphate
Tetrahydrobiopterin
5-Methyltetrahydrofolate
Aminopterin
5,10-Methylenetetrahydrofolate
Uridine triacetate
Uridine triphosphate