Racker, Efraim

The mitochondrial complex that carries out ATP synthesis is called ATP synthase or sometimes FjFo-ATPase (for the reverse reaction it catalyzes). ATP synthase was observed in early electron micrographs of submitochondrial particles (prepared by sonication of inner membrane preparations) as round, 8.5-nm-diameter projections or particles on the inner membrane (Figure 21.23). In micrographs of native mitochondria, the projections appear on the matrixfacing surface of the inner membrane. Mild agitation removes the particles from isolated membrane preparations, and the isolated spherical particles catalyze ATP hydrolysis, the reverse reaction of the ATP synthase. Stripped of these particles, the membranes can still carry out electron transfer but cannot synthesize ATP. In one of the first reconstitution experiments with membrane proteins, Efraim Racker showed that adding the particles back to stripped membranes restored electron transfer-dependent ATP synthesis. 

When Mitchell first described his chemiosmotic hypothesis in 1961, little evidence existed to support it, and it was met with considerable skepticism by the scientific community. Eventually, however, considerable evidence accumulated to support this model. It is now clear that the electron transport chain generates a proton gradient, and careful measurements have shown that ATP is synthesized when a pH gradient is applied to mitochondria that cannot carry out electron transport. Even more relevant is a simple but crucial experiment reported in 1974 by Efraim Racker and Walther Stoeckenius, which provided specific confirmation of the Mitchell hypothesis. In this experiment, the bovine mitochondrial ATP synthasereconstituted in simple lipid vesicles with bac-teriorhodopsin, a light-driven proton pump from Halobaeterium halobium. As shown in Eigure 21.28, upon illumination, bacteriorhodopsin pumped protons... 

By incorporating the purified electron-transport com- i plexes into phospholipid vesicles along with the mitochondrial ATP-synthase enzyme that is described below, Efraim Racker and his coworkers verified the capacity of the individual complexes I, III, and IV to support the formation of ATP. In figure 14.7, you can see that the flow... 

I Studies by Efraim Racker and his colleagues showed that the catalytic sites of the ATP-synthase reside in... 

S. Pontremoli 2, 18 Robert O. Poyton 17 Jack Preiss 1 Michael J. Prival 8 Daniel L. Purich 6 Efraim Racker 18 George K, Radda 10 Kari O. Raivio 2 Abburi Ramaiah 8... 

Energy Cycles in Health and Disease Efraim Racker... 

I was also influenced by Efraim Racker in the nearby Department of Bacteriology. His enthusiastic pursuit of enzyme purification was marked by success and the dictum Don t waste clean thoughts on dirty enzymes. ... 

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