Partial Resolution of the Enzymes Catalyzing Oxidative Phosphorylation

Resolution and reconstitution of ion-transport systems

1. Oxidative phosphorylation was reconstituted with a mitochondrial proton pump (oligomycin-sensitive ATPase) and segments of the oxidation chain (cytochrome oxidase or DPNH-Q1 reductase). A proton pump of bacteriorhodopsin substituted for the respiratory chain components, giving rise to light-induced ATP formation. 2. Since oxidative phosphorylation has thus become a special case of the problem of ion translocation in general, we have investigated and reconsituted other pumps. The reconstituted Ca++ pump of sarcoplasmic reticulum consists of two factors, the Ca++-dependent ATPase and a heat-stable coupling factor. 3. Other information obtained from reconstitution experiments include the role of asymmetry in organized membranes and the specificity of protein-phospholipid interaction. 4. Purified preparations of Ca++-ATPase catalyze the formation of ATP from Pi and ADP in a stepwise reaction stoichiometric with the enzyme and dependent on Ca++.

Studies of the oligomycin-sensitive ATPase from yeast mitochondria. Reconstitution of ATP-32Pi exchange in the presence of phospholipids

A purified preparation of the oligomycin-sensitive ATPase from yeast mitochondria has been shown to elicit an oligomycin- and uncoupler-senstitive ATP-32Pi exchange in the presence of phospholipids. Reconstitution was normally achieved by dialysis of an ATPase-phospholipid-cholate mixture. Following this procedure, vesicles with diameters between 200 and 1,500 A were seen by electron microscopy. As in mitochondria, ATPase activity in the reconstituted system was stimulated by a range of uncouplers which inhibited ATP-32Pi exchange. These and other findings suggest that the coupling mechanism may still be intact within the ATPase complex.