SPECIFICITY OF TRANSPORT 



port model. For observing the valine-preferring mediation in isola- 

 tion, the difficultly metabolized pseudoleucine (tertiary leucine) 

 appears a promising model amino acid. 



Figure 22 shows a possible scheme by which two transport 

 mediators discussed above could conceivably be related. The media- 



Outside 



AC 



AC 



Inside 



C + A 



Figure 22 A possible scheme for amino acid transport. C is a 

 transport site or carrier; A, an amino acid molecule. C is a more reactive 

 form of the transport site, generated perhaps by the exergonic reaction, 

 x -* y. Reaction of A with C causes not only complexing but also trig- 

 gers a structural change that places the complex CA inside the osmotic 

 barrier (indicated by the shaded band). (Note that A is used here to 

 represent the solute molecule and has nothing to do with the hypothetical 

 A site of the Ehrlich cell.) 



61 



