186 1. lODOACETATE AND lODOACETAMIDE 



uptake by mustard roots (46%-36% by 0.1 mM iodoacetate) (Wright, 

 1962), NaCl transport in frog skin (48%-0% by 1 mM iodoacetate) (Huf 

 et al., 1957), I" uptake by sheep thyroid slices (93%-34% by 1 mM iodo- 

 acetate) (Slingerland, 1955), and K+ uptake in rabbit kidney slices (93%- 

 49% by 0.33 mM iodoacetate) (Mudge, 1951). If respiration were a measure 

 of the rate of ATP generation and if all the ATP formed were available for 

 transport, some correlation might occur, but it is likely that only certain 

 fractions of the respiration are blocked by iodoacetate and that compart- 

 mentalization of ATP complicates the picture. The effects of iodoacetate 

 on transport are much more specific than could be demonstrated by over- 

 all respiratory measurements. 



A little work has been done with iodoacetate on the problem of the de- 

 pendence of transport on ATP and creatine-P levels, although the results 

 are not as clear as those obtained with uncoupling agents. Ling (1951) 

 showed that the loss of K+ from muscle due to iodoacetate and anoxia can 

 be prevented by cooling to 1°. Since metabolism is essentially stopped at 

 1° and ATP -f creatine-P remain the sole sources of energy, it was felt 

 that K+ accumulation depends on the level of these high-energy substances. 

 A correlation between cell K+ and levels of ATP and creatine-P (especially 

 ATP) was also demonstrated and iodoacetate was assumed to reduce the 

 cell K+ by reducing ATP. This was interpreted in terms of the fixed charge 

 hypothesis but this is not necessary. Whittam (1958) and Whittam and 

 Breuer (1959) have reported evidence that K+ uptake in human erythro- 

 cytes and guinea pig seminal vesicle is dependent on the level of ATP, but 

 the evidence is simply that K+ loss is accompanied by a drop in ATP. In 

 calf lens there is certainly very little decrease in ATP when Na+ extrusion 

 is markedly interfered with by 0.03-0.1 mM iodoacetate, and here some 

 more specific action on transport is likely (Kinoshita et at., 1961). The in- 

 crease in sugar transport in the rat diaphragm brought about by iodoace- 

 tate is also not correlated with significant changes in ATP or creatine-P 

 (Kono and Colowick, 1961). One of the few examples in which exogenous 

 ATP affects active transport is the uptake of thiamine by Lactobacillus 

 fermenti. The stimulation of the transport by glucose is inhibited by high 

 concentrations of iodoacetate (20-100 mM) and this is effectively counter- 

 acted by the addition of ATP (Neujahr, 1963). ATP alone has no effect on 

 thiamine uptake. 



Antagonism of Iodoacetate Inhibition by Pyruvate and Other Substrates 



If depression of transport by iodoacetate is due to a selective block of 

 the EM pathway, the addition of pyruvate (or some related substance oxi- 

 dized through the cycle) should overcome the inhibition provided (1) the 

 pyruvate can penetrate satisfactorily into the cells, and (2) the energy gen- 

 erated in the cycle can be used for the transport. Most of the reports have 



