(1) A kinetic analysis of electron donation into and through the cytochrome b-c1 complex isolated from bovine heart mitochondria has been undertaken, using trimethoquinol as the donor. (2) Rate constants of two routes of redox equilibration with quinols have been defined by kinetic measurements and with the use of the inhibitors antimycin A and myxothiazol. (3) A model of electron transfer based upon the original Q-cycle formulation is presented to explain these and related results.
