CONCEPTS AM) TERMS 



Membrane 



Outside 



Y 



Figure 7 Diagrams to represent simple transport sites: X, visualiza- 

 tion of a chemical site located so that it can receive an appropriate 

 solute molecule from either phase; once received, the solute molecule 

 can be dissociated equally well into either phase; Y and Z, sites con- 

 structed so they can receive solute molecules only from one side and 

 pass them to the other, i.e., site Y is supposed to be subject to mass- 

 action effects only from side i, site Z only from side o. 



blood cell membrane, able to receive glycerol reversibly— equally 

 well from inside or outside— thereby greatly facilitating the passage 

 of glycerol. Figure 7 crudely illustrates such a fixed site. The in- 

 herent simplicity of such a fixed site may prove to be exceptional 

 for biological transport systems. In fact, closer study of the glycerol 

 system may yet reveal some of the complexities to be described 

 later (page 21). 



Very interesting evidence is available for the nature of the 

 glycerol transport site. Cupric ion at 10~ 6 to 10 ~ 7 M will block it; 

 curiously, the effect is to protect red cells from osmotic lysis in 

 glycerol solutions. From the fact that the cupric-ion inhibition can 



19 



