The effect of hydrogen ions on the control of mitochondrial respiration.

Mitochondria incubated with substrate and orthophosphate show a low rate of respiration in the absence of ADP. Addition of ADP leads to a considerable increase in the rate of respiration (1, 2). From 2to 8-fold increases in rate are commonly observed; the extent of the increase depends on the source of the mitochondria and on the mode of their preparation. If the amount of ADP added is small, the rate of respiration returns to the previous low value when all of the ADP has been converted to ATP. The rate of respiration can also be increased greatly by the addition of uncouplers, that is, by substances which lower the efficiency of oxidative phosphorylation and, when added in sufficiently high concentrations, abolish it altogether (3). Under suitable conditions, removal of the uncouplers results in a return to the control rate (3, 4). A reversible stimulation of mitochondrial respiration by calcium ions has also been demonstrated (5, 6). The present paper shows that respiratory control of mitochondria prepared from pigeon heart can be released reversibly by addition of small amounts of hydrogen ions.