Polyphosphate kinase

In enzymology, a polyphosphate kinase (EC 2.7.4.1), or polyphosphate polymerase, is an enzyme that catalyzes the formation of polyphosphate from ATP, with chain lengths of up to a thousand or more orthophosphate moieties.

ATP + (phosphate)_n ${\displaystyle \rightleftharpoons }$ ADP + (phosphate)_n+1

Thus, the two substrates of this enzyme are ATP and polyphosphate [(phosphate)n], whereas its two products are ADP and polyphosphate extended by one phosphate moiety [(phosphate)n+1].

This enzyme is a membrane protein and goes through an intermediate stage during the reaction where it is autophosphorylated with a phosphate group covalently linked to a basic amino acyl residue through an N-P bond.

Several enzymes catalyze polyphosphate polymerization. Some of these enzymes couple phosphotransfer to transmembrane transport. These enzyme/transporters are categorized in the Transporter Classification Database (TCDB) under the Polyphosphate Polymerase/YidH Superfamily (TC# 4.E.1) and are transferases that transfer phosphoryl groups (phosphotransferases) with polyphosphate as the acceptor. The systematic name of this enzyme class is ATP:polyphosphate phosphotransferase. This enzyme is also called polyphosphoric acid kinase.