Triphosphate

Triphosphate refers to chemical species containing three phosphate groups linked by phosphoanhydride bonds. In biochemistry, the term most often denotes the triphosphate moiety in nucleoside triphosphates such as ATP, GTP, CTP, and UTP, which are central to cellular metabolism and energy transfer. Structurally, three phosphate units are arranged in a linear chain and connected by two high-energy P–O–P bonds (alpha–beta and beta–gamma linkages). The molecule carries a substantial negative charge and is highly hydrophilic, typically existing as a hydrated anion under physiological conditions.

Inorganic and physical chemistry also use the term triphosphate for the tri-phosphate anion, with the formula P3O10^5−, which can be found in polyphosphate chemistry and related systems. These species are less common in biology but can form under certain conditions and are subject to hydrolysis, yielding shorter phosphate chains or orthophosphate depending on the environment.

Biological role and properties: Nucleoside triphosphates function primarily as energy carriers (notably ATP) and as activated substrates for biosynthetic reactions and signaling. They are produced by phosphorylation of diphosphates via kinases or by metabolic pathways that furnish activated phosphate donors. The hydrolysis of the terminal phosphate group releases energy that drives many cellular processes; the overall energy yield varies with the specific triphosphate and reaction context. Nucleoside triphosphates also serve as substrates for RNA and DNA synthesis (in the case of NTPs) and participate in various signaling pathways through nucleotide exchange and hydrolysis.

See also: adenosine triphosphate, nucleoside triphosphates, polyphosphate.