phosphotransferases

Phosphotransferases are enzymes that catalyze the transfer of a phosphate group from a donor molecule to an acceptor molecule. They form a broad part of the transferases (EC class 2) and play a central role in energy metabolism and signal transduction. The most common phosphate donor is ATP, and the typical reaction yields ADP and a phosphorylated substrate. Some phosphotransferases use alternative donors, such as phosphoenolpyruvate in certain bacterial systems.

Substrate diversity is wide. Protein phosphotransferases, or protein kinases, phosphorylate proteins on serine, threonine, or tyrosine residues, thereby modulating activity, interactions, and localization. Other phosphotransferases act on small molecules, including sugars (for example, hexokinase, phosphofructokinase, and pyruvate kinase in glycolysis), as well as lipids and nucleotides. The phosphotransferase system (PTS) in bacteria provides a notable example where a phosphate relay from phosphoenolpyruvate is used to phosphorylate incoming sugars during transport.

Mechanistically, many phosphotransferases require divalent metal ions such as Mg2+ to coordinate the phosphate groups. Active-site residues help stabilize transition states and position substrates for nucleophilic attack on the donor phosphate. Kinases can be regulated by allosteric effectors, phosphorylation, and protein interactions, reflecting their roles in signaling networks. Some phosphotransferases catalyze reversible reactions, enabling rapid shifts in phosphorylation states in response to cellular conditions.

Biological roles are broad: they oversee energy capture and transfer, metabolic control, and signaling cascades that regulate growth, differentiation, and stress responses. In summary, phosphotransferases comprise a diverse set of enzymes that transfer phosphate groups to a wide range of acceptors, with ATP-dependent kinases among the most extensively studied.