However, if glutamate and malate are added together, mammalian mitochondria initially produce equal amounts of aspartate and oxoglutarate using the mitochondrial half of the malate - aspartate cycle. The aspartate and oxoglutarate porters, GOT, MDH and the respiratory chain are the only enzymes involved under these conditions. In some cases, e.g. for calcium ions, an electrical carrier is used for uptake and an electroneutral system is used for export. The two components of the proton motive force are used to drive the ion in opposite directions. This may be exploited by cells to regulate intra-mitochondrial calcium to a different value to the cytosolic concentration.
Many important metabolites show an asymmetric distribution across the mitochondrial inner membrane.
This is helpful for the operation of the citric acid cycle, and also has implications for the regulation of glycolysis and lipogenesis by phosphofructokinase and acetyl CoA carboxylase, where citrate is an allosteric effector. The most accurate studies of transport kinetics involve the rapid separation of mitochondria from their incubation medium using ultrafiltration or centrifugation through silicone oil. Large scale metabolite movements will, however, produce alterations in matrix volume through osmotic mechanisms. A qualitative estimate of transport rates can thus be obtained by measuring the changes in light scattering from a turbid mitochondrial suspension. These results were obtained from 0.5 mg liver mitochondria suspended at pH 7 in a spectrophotometer cuvette with 2.5 ml of 150 mM potassium acetate.