CLUES FROM ASSOCIATED EVENTS 



Figure 28 Hypothetical scheme for relationship between enzyme, 

 ATP, and magnesium ions. Such a positioning of magnesium-ATP on 

 the membrane is proposed by Skou to permit it to displace electrons 

 within the membrane. [From Skou, J. C. (1960), Biochim. et Biophys. 

 Acta, 42, 19; with permission^ 



nance of an activated, transport-responsive state of the membrane 

 may then be aided by the presence of high cellular levels of potas- 

 sium ion or of amino acids, or of both. 



We may note that Mitchell's scheme included an electron- 

 transport system possessing direction across a membrane, of the 

 type originally proposed by Lundegaardh (1939) as the basis of 

 anion transport. The idea that material transport is produced by this 

 system (see the writings of Conway and of Davies), without the 

 associated participation of a similarly anisotropic ATPase system, is 

 not, however, being reintroduced in this hypothesis. Mitchell's 

 proposal appears to make from the two perhaps most perplexing 

 problems of biology— solute transport and oxidative phosphorylation 

 —a single problem. 



Skou (1961) speculates that ATP acts on alkali metal trans- 

 port by being bound to the membrane by the aromatic amino group 

 and through the intermediation of a magnesium ion (Figure 28). 

 A second magnesium ion may occupy a position to make one com- 

 mon electronic system of the phosphate chain and the adenine part 

 of the ATP, with common nonlocalized electrons (Szent-Gyorgyi, 

 1957; 1960). The linkage to the membrane may then conceivably 



87 



