CONCEPTS AND TERMS 



in Table 1. The structural requirements for transport are highly 

 similar. Among the neutral amino acids with hydrocarbon side- 

 Table 1 Similarity of the Sequences of Initial Uptake Rates of Amino Acids 

 by Isolated Cells and by Intestinal Tissue a 



a All rates were observed at approximately 1 mM external concen- 

 trations. Finch and Hird (1960) have shown that the rates for uptake 

 by and transport across the intestine are closely correlated. The in- 

 hibitory effects of the amino acids on the intestinal transport of various 

 neutral amino acids increase in the same order (cf. Wiseman, 1954). 



b The results on red blood cells were obtained by Winter (1962). 



c Results on Ehrlich cells are from Oxender (1962b). 



d Results on intestine were obtained by Finch and Hird (1960). 



chains, the higher affinity (more rapid transport; stronger inhibitory 

 action) is shown in these three instances by those with large lipo- 

 philic sidechains. A discontinuity appears in each case so that the 

 lower-affinity amino acids, glycine and a-aminoisobutyric acid, suf- 

 fer much less competition than they should from the high-affinity 

 members (Akedo and Christensen, 1962a). The origin of this dis- 

 continuity and also the exceptional rate shown by alanine in the 

 Ehrlich cell will be discussed subsequently. The basic amino acids 

 represent a different family for each process, with each family show- 

 ing competition among its members but not for amino acids of 

 different net charge. These identities of behavior support the funda- 

 mental similarities of the processes. 



Agar et al. (1953; 1956) showed that everted intestinal sacs ac- 

 cumulate into the tissue the amino acids that are also concentrated 

 into a saline solution placed in the serosal compartment. Finch 

 and Hird (1960) extended this relationship to show similarity in 

 the kinetics of saturation and inhibition for the two phenomena. 



39 



