On the other hand, malic acid may be formed in the cytosol by a combined activity of phosphoenolpyruvate carboxylase (PEPC) which catalyzes carboxylation of phosphoenolpyruvate (PEP) to produce oxalacetate that is converted rapidly to malate by malate dehydrogenase
(MDH) and thus enter the mitochondria (Day & Copland,1993; Wedding, 1989).