any of a subclass of transferase enzymes that catalyze the reaction for the transfer of a free or substituted phosphate in living cells. (Research on the mechanism involved in the enzyme-catalyzed transfer of phosphate groups has established that it is not the phosphate group

but rather the phosphoryl group

that is transferred; however, the expression “transfer of phosphate groups” is current in the literature.)

Phosphotransferases are classified according to the nature of the groups that accept (incorporate) the phosphate. Thus, there are alcoholic phosphotransferases (hexokinases, phosphohexokinases), carboxylic phosphotransferases (carbamate kinase, acetate kinase), nitrogenous phosphotransferases (creatine kinase, arginine kinase), and phosphoric phosphotransferases (adenylate kinase, pyrophosphokinase). Adenosine triphosphate figures in all the reactions for the transfer of phosphate. Phosphotransferases also include the enzymes that effect what is outwardly an intramolecular transfer of phosphate (phosphoglucomutase, phosphoglyceromutase); in addition, they include pyrophosphatases, numerous nucleotidyltransferases, and enzymes that transfer two phosphate groups from such donors as adenosine triphosphate to two different acceptors.

Phosphotransferases are found in the tissues of all living organisms. Their biological importance derives from their role in phosphorylation reactions, which provide cells with energy-rich compounds. More than 200 phosphotransferases are known.