630 E. SCHOFFENIELS 



consider the permeability characters as being heterotypic expression of a 

 common biochemical system, the concept of heterotypy being used here 

 in the sense defined by Mason [20]. 



An argument in favour of this view is offered by the observation of 

 Tosteson and Hoffman [21] concerning the movement of cations in sheep 

 erythrocytes. It is known that some individual sheep have red cells with 

 high K (HK) and low^ Na concentrations, while other sheep have red cells 

 wath high Na and low K (LK) concentrations. Recent evidence given by 

 Evans (cited in [21]) suggests that the LK character is inherited as a Men- 

 delian dominant. Tosteson and Hoffman found that the active transport of 

 K is four times greater in HK cells than in LK cells, while active trans- 

 port of Na has not been identified in LK cells. Moreover, LK cells have 

 a greater passive permeability to K and smaller passive permeability to 

 Na than HK cells. Therefore it appears that a single gene controls the per- 

 meability characters responsible for both active transport and passive 

 diffusion of K and Na. 



Now to conclude. The results reported here show that the various 

 permeability characters are organized or distributed differently in the cells. 

 This distribution is in fact an essential aspect of cell differentiation. 

 Another interesting aspect of the comparative study of membrane per- 

 meability is the fact that a common biochemical system seems to be 

 responsible for the permeability characters found in living membranes. 

 Such study may help us to solve the problem of the biochemical mechanism 

 responsible for the cellular differentiation and also to narrow the gaps in 

 our knowledge concerning the structure-function relationships. 



Acknowledgments 



The author is greatly indebted to Professor M. Florkin for his continued 

 interest and stimulating discussions in the course of this work. 



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