Transport of glutamine and glutamate in kidney mitochondria in relation to glutamine deamidation

Abstract

1. In the absence of added ADP glutamine is transformed by pig kidney mitochondria to ammonium glutamate, which appears in the external medium. This reaction is stimulated only slightly by the addition of ADP, but under these conditions about 20% of the glutamate is oxidized to aspartate. 2. Externally added glutamate is oxidized to aspartate, and at about the same rate as glutamine. 3. The net rates of glutamine and glutamate influx into the intramitochondrial compartment are very slow. 4. The phosphate-dependent glutaminase activity of intact mitochondria is stimulated by the provision of energy. 5. The provision of energy also decreases the concentration of glutamate and increases the concentration of glutamine in the intramitochondrial compartment. These energy-linked changes in the glutamine and glutamate concentrations are of equal magnitude. 6. It is suggested that transport of glutamine and glutamate across the inner membrane of kidney mitochondria occurs by an obligatory exchange between the two metabolites, and is electrogenic. The existence of an electrogenic glutamine–glutamate anti-porter is proposed.