CLUES FROM ASSOCIATED EVENTS 



tinct electron donor-acceptor nearby, and thence across the mem- 

 brane by an unspecified route to the P-O-P structure of ATP (see 

 Figure 29). A cleavage of the pyrophosphate bond then donates the 

 electron to the nearest of the series of alkali metal-binding sites, 

 causing it to exchange its potassium ion for a sodium ion from the 

 interior of the cell. The electron is thereby permitted to move to 

 the next deeper site, causing the new sodium ion to progress to this 

 site in exchange for a potassium ion already there. In this way, the 

 selective affinity for sodium ion progresses through the membrane 

 to the most remote binding site, from which the sodium ion is ex- 

 changed for a potassium ion; the potassium ion comes from the ex- 

 terior as the electron is transferred to the nearby electron acceptor, 

 under the attractive action of a new ATP binding to the initial site. 



In this scheme no movement of a carrier occurs; instead only 

 the specific affinity moves as an electron migrates through the sys- 

 tem. No mode of linkage whereby ATP breakdown could cause 

 sugars or amino acids to migrate across a series of fixed points is 

 inherent in the proposal. A demonstration of the affinity change 

 with electron movement in model structures would provide mate- 

 trial support for this proposal. 



One is tempted to consider whether a system of this kind 

 could not also produce ATP synthesis in the mitochondrion, pro- 

 vided that a sufficient potential difference exists between a participat- 

 ing electron donor and a different electron acceptor. 



89 



