Inhibition of Respiration under the Control of Azide Uptake by Mitochondria

The inhibition of mitochondrial respiration by azide under various steady states was analyzed and found to be controlled by an active accumulation of azide. The azide inhibition is found to be uncompetitive with the respiratory rate. Thus the 50% inhibiting concentration of azide decreases inversely to the respiratory rate, independent of the substrate. The respiration activated by ion uptake is about 10 times more sensitive to azide than the uncoupled respiration. The respiration of particles is about 20-fold less sensitive to azide when compared to mitochondria under identical conditions (ion pumping state) and at equal respiratory rates. Azide can be demonstrated to be a permeant anion under conditions of passive swelling. An active accumulation of azide, as deduced from these results, is demonstrated by respiratory assays in sedimented mitochondria. Azide does not inhibit electron transfer to ferricyanide but rather stimulates it by activation of ion uptake. It is concluded that azide on mitochondria acts also by means of its accumulation and that its interference with energy transfer is a secondary result of its accumulation as a permeant anion.