BIOLOGICAL TRANSPORT 



seem particularly attractive. The accessibility of transport processes 

 to endocrine modification and the frequency with which such 

 effects have been demonstrated hi vivo appear further to support 

 the participation by exposed structures of the plasma membrane. 

 Although most of the approaches to the understanding of trans- 

 port have so far been indirect, direct chemical marking of the reac- 

 tive structures, or other means of monitoring their presence during 

 direct isolation procedures, appear to be a promising mode of attack. 

 The main objective, the identification of the mediating structures 

 and the demonstration of their action in isolation, remains before us. 



Speculation on the future course of transport research 



I have been urged to add a word of speculation about the 

 future. One can detect, I think, a rising excitement in the transport 

 field, which we may perhaps interpret as an optimism that a molecu- 

 lar description of transport may be reached in the present genera- 

 tion. If true, this is a strange optimism when we recall that not a 

 single binding structure engaged in transport has yet been identified, 

 and that we have only indirect indications of where the answer 

 is to be found. 



Nevertheless, I believe that one may notice a disenchantment 

 with the "stamp-collecting" stage of transport research; a decrease 

 in the satisfaction arising from the description of yet one more 

 mediated transfer showing the usual characteristics. Certainly in- 

 vestigators are placing on one another more sophisticated require- 

 ments for differentiating between transport and binding, between 

 net migration and exchange, or between transport and other access 

 processes. Furthermore, each new case of mediation tends to receive 

 rather prompt evaluation with regard to any special advantage or 

 fruitfulness that can be derived from it. 



I think one may also detect that schemes and models embodying 

 parts of the information gained by indirect means about a transport 

 system produce only tentative satisfaction. The feeling is wide- 

 spread, I believe, that definite molecular answers should be forth- 

 coming. 



How are the chemical structures producing transport then to 

 be identified and isolated? First, let me indicate my high hopes 

 that specific endgroup reagents may be discovered, such as those 

 for the reactive sites of enzymes. These should serve to mark a 



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