148 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



exchange K^- in the presence of a concentration of 2,4 dinitrophenol which 

 renders them incapable of esterifying inorganic phosphate. 



The efifect of NaF on K influx in duck cells is also compatible with this view. 

 This agent blocks glycolysis by inhibiting enolase (52). The mechanism of 

 inhibition appears to involve the complexing of Mg, which is required for the 

 reaction, as a magnesium fluorophosphate (118). NaF also inhibits ATPase 

 which requires Mg for activity. Since enolase catalyzes the conversion of 

 2-phosphoglyceric acid to phosphoenolpyruvate (52), a step which comes 

 after the primary esterification of inorganic phosphate, NaF stops glycolysis 

 when the cell has a normal or increased concentration of some phosphate esters 

 (65). Furthermore, although NaF in relatively high concentrations does in- 

 hibit phosphate uptake by human red cells (27), the effect is much less im- 

 pressive than that of lAA (66). Therefore, the failure of NaF to block K influx 

 in duck red cells is consistent with the theory that K uptake is associated with 

 the formation of a phosphate ester in the cell membrane. However, the failure 

 of arsenate as well as removal of phosphate from the medium to block K in- 

 flux is difficult to explain with this hypothesis. Therefore, in view of the multiple 

 possible sites of action of these inhibitors, it is necessary to retain a tentative 

 view regarding the mechanism of their action on K transport. Furthermore, 

 the fact that phosphate influx in chicken cells is much slower than in human 

 cells (29) while K influx is probably faster also renders a direct association be- 

 tween inorganic phosphate and K transport dubious. 



Another interpretation of these experiments involves the effects of lAA 

 and NaF on the enzyme pyruvic phosphoferase. This enzyme catalyzes the 

 reaction of phospho-enol-pyruvate (PEP) and adenosine diphosphate to 

 yield pyruvate and adenosine triphosphate (ATP). It requires j\Ig and K for 

 activity, and is inhibited by Ca and Na (2). Solvonuk and Collier (Canad. J. 

 Biochem. and Physiol. t,t,: 38-46, 1955) have recently assayed the enzyme in 

 the red cells of various species. They found that the activity of the enzyme 

 was much higher in chick than in mammalian red cells. Furthermore, they 

 found that the enzyme is completely inhibited by io~^ m/1. p-chloromercuri- 

 benzoate and about 30% inhibited by io~^ m/1. IAA, but not inhibited by 

 NaF. The analogy between these findings and our results on K transport in 

 *duck red cells is obvious. However, there are many complexities to be resolved 

 before a specific association between pyruvic phosphoferase activity and K 

 transport can be accepted. For example, Solvonuk and Collier found that the 

 enzyme was not bound to the red cell ghost but rather was found in the soluble 

 hemolysate. ATP forms rather weak complexes with Na and K but both are 

 equally stable (61). In collaboration with Drs. H. Neuberg and G. H. Mudge, 

 we have recently measured the activity of the Na and K salts of phospho- 

 enol-pyruvate with the use of a cation permeable membrane. As in the case 

 of ATP, the evidence indicated that the ratio of the activity coefficient of K 



