Role of multiple binding sites in the inhibition of NADH oxidase by piericidin and rotenone

Scatchard plots indicate that ¹⁴C-piericidin A and -rotenone bind at 2 specific sites per mole of NADH dehydrogenase in ETP, but the titer found for complex I or mersalyl-treated ETP more closely approximates 1. The curves for inhibition of NADH oxidase by piericidin and rotenone are sigmoidal; this results from an unequal contribution of the 2 specific sites to the inhibition. An unspecific binding site also contributes to the inhibition in a manner reversed by washing the particles with bovine serum albumin (BSA). In contrast, inhibition of NADH-CoQ reductase activity is due entirely to binding at specific site(s) because BSA does not restore activity.