Inhibition of maize leaf phosphoenolpyruvate carboxylase by diethyl oxaloacetate.

Diethyl oxaloacetate was found to be a competitive inhibitor of maize leaf phosphoenolpyruvate carboxylase activity with respect to the substrate phosphoenolpyruvate. The Ki values, based on total diethyl oxaloacetate, decreased with increasing pH, while the Ki values, based on the enol tautomer (average of 4 μM), were similar and independent of pH. The results suggest that inhibition is dependent on the enol tautomer. Diethyl oxaloacetate was a weak inhibitor following treatment of the enzyme with dithiothreitol; inhibition could be restored by treatment with diamide, indicating inhibition depends on the reduction state of thiol groups on the enzyme.