The present study reveals that the previously described effect of ATP-synthetase inhibition concomitant with inhibition of respiratory chain functioning may be observed at different absolute values of A$ on the mitochondrial membrane. This fact points out that the membrane potential is not a unique regulator in coupling of ATP-synthetase and respiratory chain activities. We found, using the double-inhibitor titration technique, that ATP-synthetase inhibition induces proportional inhibition of respiratory chain enzymes and vice versa respiratory chain inhibition induces proportional inhibition of ATP-synthetase. This effect is shown to exist only when osmolarity is close to 150-300 (mosM) (in the physiological range). The coupling effectivity (ADP/O) of mitochondria under these conditions is maximal. Under conditions of high osmolarity (400-600 mosM) the respiratory chain and ATP-synthetase behave as if they were coupled by bulk phase Aj&+, from the kinetic point of view.
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