Serine 774 and amino acids 296 to 437 comprise the major C4 determinants of the C4 phosphoenolpyruvate carboxylase of Flaveria trinervia.

C4 phosphoenolpyruvate carboxylases have evolved several times independently from non-photosynthetic C3 ancestral enzymes. To identify C4-specific determinants at the amino acid level the two orthologous ppcA PEPCases of Flaveria trinervia (C4) and Flaveria pringlei (C3) were used as a model system. In a previous publication [Bläsing et al., J. Biol. Chem. 275 (2000) 27917-27923] it was reported that the serine at position 774 is an invariant residue in all C4 phosphoenolpyruvate carboxylases. Here we show by swapping experiments and site-directed mutagenesis that the serine 774 and amino acids 296-437 explain two thirds of the C4 characteristic phosphoenolpyruvate saturation kinetics when investigated in the C3 background. In addition, the results indicate that the determinants functionally interact with each other.