BIOLOGICAL TRANSPORT 



hydroxyl ion migration with the movement of other ions or mole- 

 cules are apt not to be those receiving the phosphoryl group. 



In any case, in this speculative section I venture the prediction 

 that transport will be found to be produced by macromolecular 

 structures in the matrix of the membrane, and not by small, free, 

 shuttling carriers trapped in the membrane phase. The currently 

 rather mystifying swelling and contracting of mitochondria that 

 are apparently also sensitive to sulfhydryl-disulfide exchange, will, I 

 suggest, prove to be a general manifestation of the behavior of cellu- 

 lar membranes. This behavior of membranes may prove to underlie 

 many or all uphill transports and facilitated diffusions. It is also 

 possible that our present understanding of macromolecular chem- 

 istry and physics will need to be extended before we can interpret 

 the transport behavior of biological membranes. Complexities as 

 severe as those encountered in the area of muscle contraction may 

 be met here also. 



In pointing to the more direct approaches that may eventually 

 help to bring us to a molecular interpretation of transport, I do 

 not mean to say that the indirect approaches still mainly being 

 pursued have reached a level of diminishing returns. They have 

 given us most of the present conceptions of transport, and they may 

 point out even more closely where the direct attack is to be made. 



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