The main allosteric inhibitors of PEP carboxylase are the carboxylic acids malate (weak) and aspartate (strong).[1][2] Since malate is formed in the next step of the CAM and C4 cycles after PEP carboxylase catalyses the condensation of CO2 and PEP to oxaloacetate, this works as a feedback inhibition pathway. Oxaloacetate and aspartate are easily inter-convertible through a transaminase mechanism; thus high concentrations of aspartate are also a pathway of feedback inhibition of PEP carboxylase.