86 1. lODOACETATE AND lODOACETAMIDE 



bring about a loss of creatine-P to help maintain the ATP level. When the 

 ATP concentration reaches a low level, hexose phosphorylation will slow 

 and eventually cease, resulting in some cases in a rise in intracellular 

 glucose. 



(D) The fall in ATP may also reduce the total NAD and NADP concen- 

 trations by shifting the equilibria in favor of NMN, although Holzer et al. 

 (1958) observed no fall in NAD in ascites cells inhibited by iodoacetate, 

 nor did Hofmann (1960) in glycolyzing and nonglycolyzing yeast treated 

 with 20 mM iodoacetate, although the (NAD)/(NADH) ratio increased 

 markedly. 



(E) Phosphatase activity will reduce the levels of hexose phosphates and 

 release P„ this acting overall to increase P; concentration. 



(F) The steady-state levels of the intermediates distal to 3-PGDH will 

 decrease and probably drop to zero, except for pyruvate, which may remain 

 because of a deficiency of NADH to reduce it to lactate. 



(G) The pH will tend to rise due to the inhibition of metabolic proton 

 release and the breakdown of ATP and creatine-P. 



(H) It is possible, although never demonstrated, that, in some cells 

 with glucose-6-P dehydrogenase activity, gluconate-P and NADPH will be 

 formed to a limited extent. If there are substances present to oxidize the 

 NADPH, this reaction may proceed. 



(I) All reactions outside of the EM pathway which require ATP (syn- 

 theses and cell functions) will fail due to the depletion of ATP. Such ef- 

 fects can bring about a variety of secondary alterations, e.g., leakage of 

 ions from the cells, which can further modify metabolism. 



We have assumed complete inhibition of 3-PGDH. The question arises 

 as to how much 3-PGDH must be depressed before glycolysis fails, i.e., be- 

 fore ATP breakdown exceeds its generation. If 3-PHDG is inhibited 50%, 

 the balance of ATP used and formed is zero, so that presumably glycolysis 

 could continue (with lactate formation 50% depressed) if the ATP were 

 used 100% efficiently. Since the efficiency is probably never 100% and 

 since there are ATPase and phosphatases, glycolysis will proceed to de- 

 crease from 50% to eventually 0%. Thus 3-PGDH cannot be inhibited very 

 much before ATP begins to fall and glucose utilization is suppressed. Much 

 of the x>rogressive inhibition often observed in glycolytic and functional 

 measurements, which is usually attributed solely to the slow rate of reac- 

 tion of iodoacetate, is probably due to this factor of ATP balance. It also 

 explains why a tissue will fail faster when it is active in any way, i.e., when 

 it is utilizing ATP. 



