Oxaloacetate permeation in rat kidney mitochondria: pyruvate/oxaloacetate and malate/oxaloacetate translocators.

The mechanism of oxaloacetate efflux from rat kidney mitochondria has been investigated in view of its possible role both in gluconeogenesis and in transferring cytosolic reducing equivalents into mitochondria. Thus reconstruction of the malate/oxaloacetate shuttle made possible by the oxaloacetate carrier has been made. Moreover the existence of a separate translocator able to allow a bidirectional alpha-cyanocinnamate-insensitive pyruvate/oxaloacetate exchange has been ascertained. This carrier is specific of gluconeogenetic organs in particularly of kidney, where it shows a marked affinity for pyruvate (Km = 0.45 mM and Vmax = 38 nmoles oxaloacetate effluxed/min X mg mitochondrial protein at 20 degrees C). Some features of both pyruvate/oxaloacetate and malate/oxaloacetate exchanges are also described.