Abstract
The preparation of stable sonic fragments of rat-liver mitochondria capable of oxidative phosphorylation is described. These differ from sonic preparations described by others in that they are prepared very vigorous conditions, are unexpectedly stable to freezing and thawing, and show only one phosphorylation site. They rapidly oxidize a variety of substrates to give a PO ratio of approx. 1.0, corresponding to phosphorylation in the cytochrome b region of the respiratory chain. ATPase (EC 3.6.1.4), ATP-P1 exchange, and ATP-ADP exchange reactions can be demonstrated in the particles as in intact mitochondria or digitonin fragments. However, the sonic particles exhibit several unexpected properties among which are: (a) substantial Amytal-insensitive and antimycin A-insensitive respiration, (b) extremely low ATP-Pi exchange rate relative to the rate of oxidative phosphorylation, (c) inhibition of ATPase activity by Amytal or antimycin A but a large stimulation by cyanide, (d) lack of an ATP requirement for succinate oxidation after pre-treatment of the particles with uncoupling agents, (e) failure to catalyze net reduction of NAD+ or acetoacetate by succinate in the presence of ATP.
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