Proline Transport in Rat Kidney Mitochondria

Proline transport in rat kidney mitochondria was investigated both by using isotopic techniques and by spectroscopic measurements, in which proline metabolism was essentially allowed to occur. Widely used criteria for demonstrating the occurrence of carrier-mediated transport were successfully applied in both cases. Differences found in the Km and Vmax values, in pH and temperature dependence of proline transport, and in the inhibitor sensitivity demonstrate the existence of two separate translocators for proline in rat kidney mitochondria, i.e., the proline uniporter and the proline/glutamate antiporter. Efflux of glutamate via glutamate/OH− translocator following proline uptake by mitochondria was experimentally ruled out. Discussion is also made of the possible role of such translocators in proline metabolism and in the putative proline/glutamate shuttle.