A recent study demonstrated that cytosolic phosphoenolpyruvate carboxykinase (PEPCK) and NADP-malic enzyme (NADP-ME) have an important role in malate metabolism during fruit ripening (Osorio et al., 2013). PEPCK catalyze the ATP-dependent decarboxylation of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) and NADP-ME, the reversible conversion of malate and pyruvate. Here, we present the detailed protocols to measure PEPCK activity in carboxylation direction by following oxidation of NADH and to measure NADP-ME activity based upon the reduction of NADP⁺.