Studies on the characteristics of a proton pump in phospholipid vesicles inlayed with purified complex III from beef heart mitochondria.

It is well documented that the respiratory chain functions as a proton pump [l] . Two views have been put forward to describe the details of this pumping action. Mitchell’s original hypothesis described the pump as a vectorial transmembrane movement of the hydrogen and electron carriers [ 11. More recently, Papa et al. [2-41 proposed that the redox-proton pump is generated by a linkage between the oxidoreduction of the metal centers of electron carriers and the protonic equilibrium of acidic groups of the apoprotein. Consistent with this suggestion is the demonstration of a proton carrier in the Complex III region of the respiratory chain [3-51 . In this region, no classical hydrogen carriers are known [6-81. More recently, the presence of a proton pump has been demonstrated in phospholipid liposomes containing purified Complex III [9]. In the present paper we -eport a study on some properties of this proton lump, demonstrating its electrogenic nature and pH dependency.