LOCALIZATION OF THE SITE OF ACTION OF TRIALKYLTIN IN YEAST MITOCHONDRIA By KELVIN

Ligand-binding studies with labelled triethyltin on yeast mitochondrial membranes showed the presence of high-affinity sites (KD = 0.6juM; 1.2± 0.3nmol/mg of protein) and low-affinity sites (KD>45UM; 70± 20nmol/mg of protein). The dissociation constant of the high-affinity site is in good agreement with the concentration of triethyltin required for inhibition of mitochondrial ATPase (adenosine triphosphatase) and oxidative phosphorylation. The high-affinity site is not competed for by oligomycin or venturicidin, indicating that triethyltin reacts at a different site from these inhibitors of oxidative phosphorylation. Fractionation of the mitochondrial membrane shows a specific association of the high-affinity sites with the ATP synthase complex. During purification ofATP synthase (oligomycin-sensitive ATPase) there is a 5-6-fold purification of oligomycinand triethyltin-sensitive ATPase activity concomitant with a 7-9-fold increase in high-affinity triethyltin-binding sites. The purified yeast oligomycin-sensitive ATPase complex contains approximately six binding sites for triethyltin/mol of enzyme complex. It is concluded that specific triethyltin-binding sites are components of the ATP synthase complex, which accounts for the specific inhibition ofATPase and oxidative phosphorylation by triethyltin.