GKOROK T. SCOTT AND HUGH R. HAVWOOl) 53 



experimenis were carried out in which either phosphoglycerate or pyruvate 

 were added to Llnj in the dark along with the inhibitor. These intermediates 

 are, of course, normal components of the glycolytic cycle occurring below the 

 level of 3-phosphoglyceraldehy(le dehydrogenase, the site of action of iodoace- 

 tate. Representative data are presented in table 5. 



Thus pyruvate affords the cell 100% protection against the sodium increase 

 caused by iodoacetate in the dark, while it protects against potassium loss only 

 to a much smaller extent. Phosphoglycerate, on the other hand, offers essen- 

 tially no protection against sodium increase hut allows a very significant pro- 

 tection against potassium loss. 



Table 5. Protective influence of pyruvate and phosphoglycerate when given 



WITH iodoacetate 



phoglycerate 



* Experiment run for 5 hr. in the dark (Ulva). 

 t E.xj^eriment run for 6 hr. in the dark {Ulva). 



It might be suggested from the e.xperiments with exogenous pyruvate and 

 phosphoglycerate that the two transport mechanisms are energetically coupled 

 to metabolism at different points in the glycolytic and/or respiratory cycles. 

 Indeed, such a possibility is in line with some of the other experimental results 

 l)resented here. But to detine precisely where these points of coupling are (and 

 there is no good reason at present to believe that there may not be more than 

 one for each 'pump') is not possible on the basis of the existing data. We 

 might say that energy for the 'potassium pump' seems to come from below the 

 level of phosphoglycerate, while the 'sodium pump' seems to be coupled to the 

 metabolism of pyruvate or a product of its metabolic degradation. 



Action of 4,6-Dinitro-o-Cresol. Since energy apparently is necessary to ac- 

 complish potassium accumulation and sodium secretion and since the high 

 energy phosphate bond may be the principal type of energy currency the cell 

 uses, the action of 4,6-dinitro-o-cresol (DNC) was investigated. This agent, 

 like related substituted phenols, effectively dissociates aerobic respiration from 



