BIOLOGICAL TRANSPORT 



nately, intermediate levels of glucose were not tested, so that the 

 attention of Ege and his associates fell on the factor of the presence 

 or absence of electrolytes in the suspending medium rather than 

 on the factor of glucose concentration per se. 



What one frequently observes is that, as the solute level is in- 

 creased, the flux eventually ceases to increase but instead reaches a 

 maximal value. This result implies that a reaction with a chemical 

 structure or site present in a limited amount is necessary to transport, 



Equilibrium cone, hypoxanthine, mM 



Figure 5 Inhibitory action of hypoxanthine on labeled uric acid 

 entry from 0.11 M phosphate solution into red blood cells containing an 

 equivalent concentration of unlabeled uric acid. Even high levels of 

 hypoxanthine do not abolish one component of the entry. [From Over- 

 gaard-Hansen, K., and Lassen, U. V. (1959), Nature, 184, 553; with 

 permission.] 



16 



