Phosphotransfer

Phosphotransfer is the transfer of a phosphate group from a donor molecule to an acceptor molecule. In biology, it is a fundamental mechanism for energy transfer, regulation, and signaling. Most phosphotransfer reactions are enzymatically catalyzed by kinases or phosphotransferases, though some occur spontaneously under appropriate conditions.

Common phosphate donors include ATP, GTP, phosphoenolpyruvate, and acetyl phosphate. Acceptors can be proteins, sugars, lipids, nucleotides, or small molecules. Protein phosphorylation is among the most studied forms of phosphotransfer, where kinases transfer the γ-phosphate from ATP to serine, threonine, or tyrosine residues on target proteins; phosphatases can reverse the modification. This reversible process modulates enzyme activity, interactions, and protein localization, playing key roles in signaling pathways and cellular regulation.

Substrate-level phosphorylation is another form, in which a substrate transfers a phosphate to ADP to form ATP. In glycolysis, for example, a high-energy phosphate from a substrate is transferred to ADP to yield ATP, with the substrate becoming a different product in the process.

In bacteria, phosphotransfer systems illustrate a specialized form of phosphotransfer called a phosphorelay. Phosphate is transferred from phosphoenolpyruvate to a series of proteins, often including histidine and aspartate residues, ultimately affecting gene expression and metabolism in response to environmental cues.

Overall, phosphotransfer couples energy flow to information processing in cells, enabling rapid and tightly controlled responses to physiological conditions.