Abstract
Phosphoenolpyruvate carboxylases from various organisms contain two conserved lysine residues. In the C4 dicot Flaveria trinervia, one of these residues is Lys600. Converting this Lys600 to Arg600 or Thr600 mainly increased the K m values and but had minimal effect on the V max. The K m for PEP, Mg2+ increased by up to 3‐fold in Arg600 and Thr600 but the K m (HCO3 ) increased 9‐fold in Thr600, suggesting that Lys600 might be associated with bicarbonate‐binding. This lysine was not obligatory for enzyme activity although the wild‐type protein showed higher activity at physiological pH and was less inhibited by malate than the two mutants.

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