Fosfoanhydrid

Fosfoanhydrid, or phosphoanhydride in English, designates a class of chemical compounds characterized by one or more phosphoanhydride bonds, typically represented as P-O-P, linking two phosphate units. The term is most often encountered in biochemistry to describe the high-energy bridges between phosphate groups in nucleotide triphosphates and related polyphosphates.

In chemistry, a phosphoanhydride bond forms by condensation between two phosphate groups with the loss of a water molecule. The resulting phosphoanhydride linkage is highly reactive toward hydrolysis, a property exploited by biological systems to drive endergonic processes.

In biology, phosphoanhydride bonds are the primary energy-carrying links in ATP and GTP. Hydrolysis of the gamma-phosphoanhydride bond in ATP to ADP and inorganic phosphate releases a key portion of cellular energy; further hydrolysis of PPi to two inorganic phosphate units can provide additional energy in metabolic pathways. Pyrophosphate itself is a simple phosphoanhydride and is routinely produced and consumed in biosynthetic reactions.

Formation of phosphoanhydride bonds occurs during the synthesis of nucleotide triphosphates and polyphosphates, often through enzymatic steps that couple condensation to energy input or to subsequent hydrolysis. These bonds are distinct from phosphoester and phosphodiester bonds, which join phosphate groups to sugars or to proteins.

Notable examples include ATP, GTP, and inorganic pyrophosphate (PPi). Phosphoanhydride chemistry is also relevant in bioenergetics, signaling, and polymerization processes. See also pyrophosphate, ATP, GTP, and polyphosphate.