Spontaneous modification of the oxoglutarate translocator in vivo

In studying the oxoglutarate translocator of rat-heart mitochondria over many years, we have observed an unexpected decrease in its efficiency. It has been divided by 2.48 +/- 0.07, (S.E.M.) for the exchange of external oxoglutarate for internal malate at 2 degrees C when the internal-malate concentration is 4 mM and is accompanied by an increase in its concentration (multiplied by 1.61 +/- 0.02, S.E.M.). The affinity of the external sites of the translocator for the external oxoglutarate is unchanged as well as the binding and kinetic cooperativities of the external oxoglutarate. This shows that the external side of the translocator has not been modified and suggests that its central part has not been modified either. The apparent Michaelis constant of the internal malate is increased (multiplied by 1.74 +/- 0.23, S.E.M.) suggesting that the translocator has been modified on its matricial side. Some control experiments show that a change in the diet of the rats, despite its effect on the fatty-acid content of the mitoplasts, is probably not responsible for the observed modification. As it is nevertheless very likely that changes of the oxoglutarate translocator have occurred in vivo, it is proposed that the observed modification has a genetic origin. The existence of two antagonist changes which are not directly related suggests that one of them is a response of the organism against the other; thus the oxoglutarate translocator may play a regulatory rôle in certain physiological conditions.