BIOLOGICAL TRANSPORT 



intestine, although this situation must be kinetically more com- 

 plex. In Figure 18 the rates at 1-m/Vf levels are plotted from the data 

 of Finch and Hird (1960) against those obtained at 10 mAf. The 

 tendency for the sequence of rates to be reversed (excepting for 

 glycine) is obvious. The exceptional positions of glycine and 

 a-aminoisobutyric acid on such a plot have been mentioned earlier. 

 More complex kinetic treatment has been proposed for the 

 cases in which an enzyme may be necessary for the formation and 

 dissociation of the solute-carrier complex (Wilbrandt and Rosen- 

 berg, 1961). 



14 



12 



10 



« 8 



<u 



« 



4-1 



D 6 



r-LEU 



PRO 

 HIS 



ASPNH, 

 SER 



GLY 



20 



40 



60 



Uptake rate at 10 mM 



Figure 18 Relationships between the rates of uptake of amino 

 acids at 1- and \0-mM levels by intestinal tissue. [Data of Finch, L. R., 

 and Hird, J. F. R. (1960), Biochim. et Biophys. Acta, 43, 268.] 



48 



