48 ALBERT L. LEHNINGER 



are recognizable and are susceptible to assay, purification, and use in 

 reconstruction experiments. Furthermore, applications of physical 

 methods to isolated proteins of the membrane, particularly the coupling 

 enzymes, may provide direct approaches to study of the "mechano- 

 enzyme" nature which we have postulated to account for the swelling- 

 contraction phenomena. 



While our knowledge of oxidative phosphorylation and of the mech- 

 anism of mitochondrial swelling and contraction is still fragmentary and 

 there are many loose ends still to be accounted for satisfactorily, it is 

 evident that these complex chemical and mechano-chemical activities of 

 the mitochondrial membrane are approachable on the molecular level and 

 can be at least partly reconstructed or reconstituted. It is of course im- 

 portant to examine these phenomena as they occur in intact mitochondria 

 because of the extraordinary possibilities they afford for physiological 

 control mechanisms, however it is clear that the greatest challenge and the 

 most significant developments toward full knowledge of the molecular 

 biology of the mitochondrion can be expected to come from examination 

 of the separate molecular entities participating in these complex reactions. 



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