Experimental demonstration of respiratory control

Oxygen uptake is monitored in carefully prepared coupled mitochondria.

The addition of an exogenous oxidizable substrate (glutamate) stimulates respiration only slightly, unless ADP + Pi is added as well.

Both ADP additions represent limiting amounts; the second addition is twice the amount of the first, to show that the magnitude of oxygen uptake is stoichiometric.

The slow oxygen uptake at the beginning results from endogenous substrates in the mitochondria.

ADP stimulates respiration only until all of the ADP + Pi has been converted to ATP.

Oxygen uptake is recorded in moles O, because one pair of electrons reduces one atom of O, not one molecule of O2.