InterPro domain: IPR017409

This entry represents pyruvate Pi dikinase (PPDK) regulatory protein found in chloroplasts, which acts as a bifunctional serine/threonine kinase ( 2.7.11 ) and a phosphorylase ( 2.7.4 ) [ 1 ]. This enzyme is involved in the dark/light-mediated regulation of PPDK by catalysing its phosphorylation/dephosphorylation. Dark/light-induced changes in stromal concentrations of the competing ADP and Pi substrates govern the direction of the reaction. In the dark, it phosphorylates the catalytic intermediate of PPDK (PPDK-HisP), thereby inactivating it. Light exposure induces the phosphorolysis reaction that reactivates PPDK. Unlike the kinase function which can utilise either Thr or Ser as a target, the phosphorylase function has a strict substrate requirement for threonyl phosphate [ 2 , 3 , 4 ].

1. Cloning and expression of maize-leaf pyruvate, Pi dikinase regulatory protein gene. Biochem. Biophys. Res. Commun. 345, 675-80
2. Regulation of C4 photosynthesis: identification of a catalytically important histidine residue and its role in the regulation of pyruvate,Pi dikinase. Arch. Biochem. Biophys. 231, 175-82
3. Sequence of the phosphothreonyl regulatory site peptide from inactive maize leaf pyruvate, orthophosphate dikinase. J. Biol. Chem. 263, 6683-7
4. Further analysis of maize C(4) pyruvate,orthophosphate dikinase phosphorylation by its bifunctional regulatory protein using selective substitutions of the regulatory Thr-456 and catalytic His-458 residues. Arch. Biochem. Biophys. 375, 165-70