598 PETER MITCHELL 



catalysts. I hope to develop this interesting and important aspect of 

 translocation catalysis on another occasion. 



My purpose in concluding with these rather brief thoughts on what I 

 have called vectorial metabolism was two-fold. First, these thoughts add 

 something to our conception of the intimate relationship between transport 

 and metabolism; and second, they pose a most important experimental 

 question. The activities of the translocation catalysts in their natural 

 situation in membranes or other anisotropic complexes are not strictly 

 comparable to their activities in the homogeneous solutions in which we 

 are accustomed to isolate and study them. How, then, can we proceed to 

 identify the translocation catalysts and demonstrate the molecular mechan- 

 ism of their activity ? I believe that the only satisfactory answer to this 

 question is to be found in the fourth method of approach to the analysis of 

 membrane transport that I mentioned at the beginning of this paper. We 

 must strive to set up "synthetic" or reconstituted membrane systems with 

 which we can study directly both the processes of transfer (in the normal 

 biochemical sense) and the processes of translocation, catalyzed by 

 enzymes and catalytic carriers under anisotropic conditions that can be 

 controlled and measured. 



I am indebted to Dr. Jennifer Moyle for helpful general discussions 

 during the preparation of this paper, to Dr. J. Dainty for help in describing 

 the electrochemical activity in relation to escaping tendency, and to Dr. 

 P. H. Tuft for suggesting the word "substratum" as a synonym for 

 enzyme-locator. I am also glad to acknowledge grants from the Nuffield 

 Foundation in aid of this work. 



References 



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