Molecular Aspects of Structure-Function Relationship in Mitochondrial H + -ATPase
Among various ATPases involved in active transport across biological membranes, the proton translocating ATPase (H+-ATPase) of mitochondria, chloroplasts, and bacteria represents the most complicated enzyme complex. In spite of such a tremendous effort, the molecular mechanism of coupling between H+-translocation and ATP synthesis catalyzed by H+- ATPase remains unclear. The chapter focuses on the subunit composition and structural organization of mitochondrial H+-ATPase, particularly in the light of the knowledge of H+-ATPases from other energy-transducing membranes where a pronounced progress has recently been reached. IIt analyzes the primary event in enzyme function, i.e., proton translocation and the overall mechanism of coupling of proton transport with catalytic function of mitochondrial H+-ATPase. All preparations of isolated H+--ATPase from mitochondria catalyze oligomycin and DCCD- sensitive hydrolysis of ATP, which can be stimulated by the addition of phospholipids. Most preparations also catalyze the ATP-Pi exchange reaction sensitive to oligomycin, DCCD, and uncouplers.