Influence of 8-azido-ATP and other anions on the activity of cytochrome c oxidase.

The effect of ATP and other anions on the kinetics of cytochrome c oxidation by reconstituted bovine heart cytochrome c oxidase was investigated. The following results were obtained: (1) ATP and other polyvalent anions increase the Km for cytochrome c and the Vmax (if assayed by the photometric method). The magnitude of the effect is proportional to the charge of the anion as follows from the series of increasing effectiveness: Pi less than AMP less than ADP less than PPi less than ATP less than PPPi. (2) The kinetic effects are obtained in the millimolar physiological concentration range. (3) The kinetic changes are not saturated at high concentrations. (4) A specific interaction site for ATP at the cytosolic domain of the enzyme is concluded from the increase of Km for cytochrome c after photolabelling of proteoliposomes with 8-azido-[gamma-32P]-ATP, which is protected by ATP but not by ADP. (5) No specific "binding site" for ATP could be identified by photolabelling with 8-azido-[gamma-32P]-ATP. The labelling is only partly protected by ATP or ADP.