KKXST C. HUF 233 



the last member of the family of electron carriers in the membrane (indicated 

 below by asterisk) rotates therein; whereupon, the electron is handled by the 

 oxidizing enzymes of the cytoplasm (Md = cytochrome oxidase). 



Symbolically, Conway's theory of the mechanism of active sodium transport 

 may be given as follows (2): 



cytoplasm i/2CtH, + .Ma + Na+ = i/2Ct + ]\Ia-Na+ + H+ 

 membrane ]\Ia-Na+ + ^Ib = Ma + INIb" + Na+ — * (extruded) 

 membrane Mb~ + Mc* = Mc~ + ]\Ib 

 membrane- 

 cytoplasm Mc- + Md = Md- + Mc 

 cytoplasm Md" + i 4O, + H+ = Md + 1/2H0O 



Electroneutrality is secured since chloride ion follows sodium passively from the 

 left to the right side in this scheme. Thermodynamical aspects of this scheme 

 were also discussed by Conway (2). 



This concept gives a satisfactory explanation of the mechanism whereby ions, 

 such as sodium ion, could be translocated and accumulated. Furthermore, it 

 clearly shows the dependence of ion transport on oxidative reactions. The in- 

 hibitory effect of cyanide on active ion transport is readily explained. There is 

 at present, however, no experimental evidence that would substantiate the 

 assumption of a chain of reactions involving sodium ion, as outlined above. 



DUAL PUMP HYPOTHESIS OF ACTIVE SODIUM TRANSPORT IN FROG SKIN 



From what has been said above, it would seem that Conway's theory may 

 best explain active sodium transport in frog skin. The question of whether, in 

 frog skin, the utilization of free energy available in the electron jumps of a 

 redox system is a direct one, as the above scheme implies, or an indirect one, 

 must be approached, however, with caution. Repeatedly it was found that 

 active ion transport in frog skin can be inhibited by 2,4-dinitrophenol, with no 

 reduction in oxygen consumption of skin; in fact, oxygen uptake was increased 

 (9, 44). This points to the participation of energy rich phosphate as an energy 

 source for driving an ion transporting mechanism. One mechanism, however, 

 does not exclude the other. The complex morphology of the skin is quite sug- 

 gestive of sodium ions eventually becoming involved in several metabolic 

 processes during their passage from the epithelial side towards the corium side 

 of the skin. 



Proposed for consideration is the possibility of a dual pump mechanism in 

 skin, characterized by two different types of ion pumps which are spatially 

 separated and which are working sequentially. 



i) An ' adsorplion-desorption pump' is visualized as maintained by energy-rich 

 phosphate and designed to keep sodium ions desorbed and potassium ions ad- 

 sorbed at the cell surfaces or at surfaces within the cell (mitochondria; Golgi 



