Bifunctional serine/threonine kinase and phosphorylase involved in the regulation of the phosphoenolpyruvate synthase (PEPS) by catalyzing its phosphorylation/dephosphorylation. [pyruvate, water dikinase] + ADP = [pyruvate, water dikinase]-phosphate + AMP + H(+) [pyruvate, water dikinase]-phosphate + H(+) + phosphate = [pyruvate, water dikinase] + diphosphate Homotetramer. Belongs to the pyruvate, phosphate/water dikinase regulatory protein family. PSRP subfamily.