It is further believed that malate acts as a feedback inhibitor of kinase expression levels, and as an activator for phosphatase expression (transcription).[12] Since oxaloacetate is converted to malate in CAM and C4 organisms, high concentrations of malate activate phosphatase expression - the phosphatase subsequently de-phosphorylates and thus de-actives PEP carboxylase, leading to no further accumulation of oxaloacetate and thus no further conversion of oxaloacetate to malate.