Regulatory Dephosphorylation of Catalytic His‐P of Inactive PPDK in Maize

Plant pyruvate phosphate dikinase (PPDK) is a major enzyme involved in C4 photosynthesis. It undergoes up/down (activation/inactivation) regulation in response to light by the enzyme PPDK Regulatory Protein (RP) via reversible phosphorylation. The rate of dephosphorylation of inactive p‐PPDK depends on the removal of the catalytic His‐P from the active site of PPDK. The mechanism involved in this removal is remains to be discovered. We hypothesized that an adjacent Ser residue participates in the His‐P dephosphorylation. We explored this hypothesis by producing a site directed mutation converting wild‐type (WT) Ser into Ala. Phosphorylation/inactivation of mutant (MT) PPDK by RP was unchanged. However, a preliminary experiment showed a higher rate of dephosphorylation (activation) in the MT vs. WT. Thus, this preliminary data showed the Ser residue may be involved in a yet to be discovered His‐P dephosphorylation mechanism.