STUDIES ON THE INHIBITION OF THE MITOCHONDRIAL ATP-ase BY REDUCTION OF THE RESPIRATORY CHAIN
The effects of inhibition of the electron transport system on the stimulation of the ATP-ase reaction in liver and rat-heart mitochondria by dinitrophenol were studied. Cyanide at concentrations 10−3M and higher effectively reduced the stimulation of ATP-ase by dinitrophenol. A similar but less striking inhibition was observed for rat-heart sarcosomes. This ATP-ase reaction was also inhibited in the presence of 10−4M cyanide with glutamate, β-hydroxybutyrate, DPNH, and succinate as reductants of the respiratory chain. Anaerobiosis also caused a substantial decrease in the ATP-ase reaction. In all instances, complete inhibition of the ATP-ase reaction could not be achieved when the respiratory chain was reduced. The magnesium-stimulated ATP-ase of rat-heart sarcosomes, of aged mitochondria, and of the Keilin–Hartree heart-muscle preparation was insensitive to reduction of the carriers suggesting that this reaction may constitute only part of the total ATP-ase reaction. The compatability of the various mechanisms of oxidative phosphorylation with these results is discussed.
Stimulation of electron flow in the reaction center of photosynthetic electron transport system by bicarbonate in cell-free extract of Chlorobium limicola f. thiosulfatophilum.