A fluorescent derivative of the oligomycin-sensitivity conferring protein (acrylodan-OSCP). Evidence for polarity changes in the environment of CYS118 of OSCP upon binding to mitochondrial F1.

The fluorescent probe, 6-acryloyl-2-dimethylaminonaphtalene (acrylodan) was reacted with the oligomycin-sensitivity conferring protein (OSCP). Acrylodan bound covalently to the single cysteinyl residue of the protein. Acrylodan-OSCP was fully competent in conferring oligomycin sensitivity to the mitochondrial F0-F1 ATPase complex. The fluorescence emission peak of acrylodan-OSCP was blue-shifted compared to that of an acrylodan-mercaptoethanol adduct, which means that acrylodan experiences a hydrophobic environment in OSCP. Binding of acrylodan-OSCP to the isolated F1 was accompanied by a red shift of fluorescence. It was achieved in less than 1 s at 25 degrees C. The titration curve revealed one high affinity OSCP binding site per F1. Acrylodan-OSCP appears to be an interesting tool for studying the dynamics of structural changes within the mitochondrial ATPase complex.