78 1. lODOACETATE AND lODOACETAMIDE 



and essentially no glucose was taken up, so little of the phosphate ester 

 could be formed, although a greater fraction of the glucose metabolized 

 went to fructose- 1,6-diP in the inhibited cells. Some fructose- 1,6-diP accu- 

 mulated aerobically. 



The changes in erythrocytes are basically the same but differ in details 

 from the cells previously discussed, especially with respect to 2,3-diphos- 

 phoglycerate which is normally present in relatively high concentrations, 

 lodoacetate causes a fall in the level of 2,3-diphosphoglycerate and a simul- 

 taneous rise in inorganic phosphate in human erythrocytes (Prankerd and 

 Altman, 1954), but since 30 mM was used it is difficult to attribute the re- 

 sults to a selective action of 3-PGDH. More striking results (see accompany- 

 ing tabulation) with a much lower iodoacetate concentration were obtained 



Concentration of phosphates 



Compound % Change 



Control lodoacetate (0.5 mM) 



- 27 



- 70 



+556 



by Mills and Jones (1961), who suggested that although iodoacetate would 

 prevent ATP synthesis from glucose, the 2,3-diphosphoglycerate might be 

 hydrolyzed to 3-phosphoglycerate which could form ATP during conversion 

 to pyruvate. The 2,3-diphosphoglycerate certainly disappears but the ATP 

 drops to very low levels, so that the authors concluded that this mechanism 

 for ATP generation is not very important for some reason. The decrease in 

 fructose-l,6-diP is surprising and may be due to the long incubation period 

 (5 hr), the low levels of ATP for glucose phosphorylation, and phosphatase 

 activity. Somewhat different results were reported by Gerlach and Liibben 

 (1959) using shorter incubations (45 min), and here fructose-l,6-diP and 

 triose-P accumulate typically, while there is little change in 2,3-diphospho- 

 glycerate (Fig. 1-8). Glucose is normally metabolized in erythrocytes about 

 as rapidly as it enters the cells and the steady-state glucose concentration 

 is low (unless external glucose concentration is high), but in the presence 

 of 1 mM iodoacetate the intracellular glucose rises markedly — e.g., from 

 16 to 393 mg% in around 5 hr — in rabbit erythrocytes (Laris, 1958), 

 showing that phosphorylation of glucose is interfered with, although wheth- 

 er this is a direct action or due to ATP depletion is not known. An in- 

 crease in intracellular glucose to the same concentration as in the medium 

 has also been observed in isolated lymph node cells incubated with 1 milf 

 iodoacetate (Helmreich and Eisen, 1958). Avian erythrocytes are much less 



