Describing a metabolic pathway that replenishes an intermediate in one of the main metabolic pathways. For example, some Krebs cycle intermediates function not only in energy metabolism but are also used as building blocks for the biosynthesis of various compounds. Unless these intermediates are replaced, these crucial pathways will slow down or halt completely. In plants, mitochondrial oxaloacetate, which is a Krebs cycle intermediate used for the synthesis of amino acids, can be replenished by the conversion of phosphoenolpyruvate derived from glycolysis in the cytosol. The cytosolic oxaloacetate is then reduced to malate, which enters the mitochondria, where it is reoxidized to oxaloacetate.