Phosphoryl Transfer Reactions

Abstract

Abstract Phosphoryl transfer is the name given to the chemical process of the transfer of the phosphoryl group ( PO 3 ) from a phosphate ester or anhydride to a nucleophile. Nucleophilic attack by water on a phosphate monoester gives the hydrolysis product inorganic phosphate. This net dephosphorylation reaction is the process catalysed by phosphatases. Although the reaction is thermodynamically favourable, it has a very high kinetic barrier, making the uncatalysed hydrolysis of phosphate esters extremely slow. The opposite process, the formation of phosphate esters, is termed phosphorylation and is accomplished in biological systems by kinases. The balance between phosphatase and kinase activities in biology serves to regulate the phosphorylation level of many enzymes and other proteins in the cell, forming an important regulatory mechanism that is found throughout the biological world. Key Concepts The post‐translational phosphorylation levels of proteins are regulated by the complimentary actions of phosphatases and kinases. The uncatalysed hydrolysis of phosphate esters has a very high kinetic barrier, making phosphatases among the most efficient enzymes known. The various families of phosphatases use different catalytic machinery and mechanisms to carry out phosphate ester hydrolysis.