1. Tributyltin at concentrations of approx. 1nmol/mg of protein induces respiratory control and lessens the protein permeability of coupling-factor-deficient submitochondrial particles. 2. At these concentrations or lower, it increases the P/O ratio of the particles to a small extent and inhibits the adenosine triphosphatase activity without greatly increasing its sensitivity to uncoupling agents. 3. It fails to stimulate ATP-driven reversed electron transport or transhydrogenase, but stimulates the transhydrogenase driven by aerobic succinate oxidation. 4. The results indicate that, unlike oligomycin, tributyltin does not discriminate between damaged and intact ATP-synthesizing complexes. 5. The relationship between the oligomycin- and tributyltin-binding sites is discussed.
