Phylogenic and phosphorylation regulation difference of phosphoenolpyruvate carboxykinase of C3 and C4 plants.

In C4 plants, phosphoenolpyruvate carboxykinase (PEPCK) plays a key role in the C4 cycle. PEPCK is also involved in gluconeogenesis and is conserved in both lower and higher organisms, including in animals and plants. A phylogenic tree constructed from PEPCK sequences from bacteria to higher plants indicates that the C4 Poaceae PEPCKs are conserved and have diverged from the PEPCKs of C3 plants. The maximum enzymatic activities of wild-type and phosphorylation mimic PEPCK proteins indicate that there is a significant difference between C3 and C4 plant PEPCKs. The conserved PEPCK phosphorylation sites are regulated differently in C3 and C4 plants. These results suggest that the functions of PEPCK have been conserved, but that sequences have diverged and regulation of PEPCK is important in C4 plants, but not in herbaceous and, in particular, woody C3 plants.