Enzymes of the mitochondrial respiratory chain serve as proton pumps, usingthe energy made available from electron transfer reactions to transport protonsacross the inner mitochondrial membrane and create an electrochemical gradientused for the production of ATP. The ATP synthase enzyme is reversible and canalso serve as a proton pump by coupling ATP hydrolysis to proton translocation.Each of the respiratory enzymes uses a different strategy for performing protonpumping. In this work, the strategies are described and the structural basesfor the action of these proteins are discussed in light of recent crystalstructures of several respiratory enzymes. The mechanisms and efficiency ofproton translocation are also analyzed in terms of the thermodynamics of thesubstrate transformations catalyzed by these enzymes.