dikinase

Dikinase is a term used in biochemistry to describe a class of kinases that perform two phosphorylation-related steps within a single catalytic cycle. In this sense, dikinases are distinguished from monokinases by having two catalytic activities or two phosphotransfer sites, enabling a coordinated transfer of phosphate groups from a high-energy donor to a substrate through an enzyme-bound intermediate. The best-known example is pyruvate phosphate dikinase (PPDK), which links glycolysis and gluconeogenesis in organisms that regenerate phosphoenolpyruvate (PEP) from pyruvate.

The mechanism of dikinases typically involves a phosphoenzyme intermediate and two sequential phosphorylation events. An ATP-derived phosphate is often transferred to the enzyme itself, creating a phospho-enzyme intermediate, which then passes a phosphate to a second substrate or to inorganic phosphate, leading to the formation of a high-energy product such as PEP. The overall reaction for PPDK, in many organisms, is pyruvate + ATP + Pi ⇌ PEP + AMP + PPi. This two-step phosphate transfer allows the enzyme to couple energy from ATP to substrate activation in a single catalytic cycle.

Dikinases play important roles in metabolism. In plants, PPDK is pivotal for the C4 photosynthetic carbon-concentrating mechanism, regenerating PEP in mesophyll cells. In bacteria and archaea, related dikinases participate in gluconeogenesis and carbon flux, providing flexibility under varying energetic and environmental conditions. Related enzymes include phosphoenolpyruvate synthase (PEPS) and other multi-domain dikinases.

See also: pyruvate phosphate dikinase, phosphoenolpyruvate synthase.