pyrophosphokinase

Pyrophosphokinase, often referred to as a pyrophosphorylase, denotes a class of enzymes that catalyze the transfer of a pyrophosphate group from a nucleoside triphosphate to an acceptor substrate. In many reactions the donor is a nucleoside triphosphate such as ATP or UTP, and the products include a pyrophosphorylated substrate and inorganic pyrophosphate (PPi). The exact donor and acceptor vary among enzymes in this broad group.

A characteristic and well-studied example is ADP-glucose pyrophosphorylase, which converts ATP and glucose-1-phosphate into ADP-glucose and PPi. ADP-glucose then serves as a precursor for starch and glycogen biosynthesis in plants and some bacteria. Another prominent example is UDP-glucose pyrophosphorylase, which forms UDP-glucose from glucose-1-phosphate and UTP, supplying a key substrate for cellulose and other polysaccharide biosynthesis. The pyrophosphorylase family also includes enzymes that act on other sugar phosphates and nucleotide donors, reflecting its central role in nucleotide sugar metabolism.

Physiological roles of pyrophosphokinases span carbohydrate, cell wall, and cofactor biosynthesis. They couple energy charge to the production of activated sugar donors and other activated substrates, enabling polymer formation and metabolic regulation. Regulation is often complex and can involve allosteric effectors, feedback from product levels, and tissue- or organ-specific expression.

In nomenclature, these enzymes are sometimes grouped under nucleotidyltransferases (EC 2.7.7.x) or described as pyrophosphorylases. While the term pyrophosphokinase remains in use, modern classifications emphasize their enzymatic mechanism—transfer of a pyrophosphate moiety to a substrate using a nucleoside triphosphate donor.