Localization of acidic residues involved in the proton pumping activity ofthe bovine heart mitochondrial bc(1) complex

Chemical modification of carboxyl residues in polypeptide subunits of the m itochondrial bc(1) complex causes a decoupling effect, that is inhibition o f the proton plumping activity, without affecting the rate of electron tran sfer to ferricytochrome c. The study presented here is aimed at localizing and identifying the residues whose modification results in decoupling of th e complex. Glutamate-53 in subunit IX (:the DCCD-hinding protein) and aspar tate-166 in the Rieske iron-sulfur protein are the residues modified by N,N '-dicyclohexylcarbodiimide (DCCD) and N-(ethoxycarbonyl)-2-ethoxy-1,2-dihyd roquinoline (EEDQ), respectively. The results obtained also suggest that th e carboxy-terminal sequence of the Core protein TI, which is fairly rich in acidic residues, may also play a role in the vectorial proton translocatio n activity of the complex. (C) 1999 Federation of European Biochemical Soci eties.