80 1- lODOACETATE AND lODOACETAMIDE 



inhibited less than glycolysis by 0.05 mM iodoacetate in retinal extracts 

 (57% and 91%, respectively). More recently Brady et at. (1961) have re- 

 ported that, whereas iodoacetate at concentrations around 0.1 mM inhib- 

 its anaerobic glycolysis from added glucose in yeast, the endogenous gly- 

 cogenolysis activated by azide is either unaffected or actually stimulated. 

 They felt that this lends support to the idea that iodoacetate depresses 

 yeast fermentation by an action at some step between glucose and fructose- 

 1,6-diP, rather than entirely on 3-PGDH, perhaps by preventing glucose 

 assimilation or inhibiting hexokinase. 



Although Yamasaki (1930) found the fermentation of fructose- 1,6-diP 

 by yeast to be inhibited strongly by 0.9 mM iodoacetate (probably as much 

 as the fermentation of glucose), others have found the fermentation of fruc- 

 tose-l,6-diP to be less sensitive. Beevers (1950) reported that 0.1 mM iodo- 

 acetate inhibits aerobic glucose fermentation 82.5% and fructose- 1,6-diP 

 fermentation 15% at 40 min. and presented curves showing that glucose 

 fermentation is well inhibited between 0.01 and 0.1 mM whereas fructose- 

 1,6-diP fermentation is essentially unaffected. He postulated that some en- 

 zyme between glucose and fructose- 1,6-diP must be sensitive to iodoacetate. 

 On the other hand, Kelly et al. (1955) found the oxidation of fructose-1,6- 

 diP by adrenals to be inhibited more than the oxidation of hexoses or hexose 

 phosphates (see accompanying tabulation). This is to be expected if an 



active pentose-P pathway exists, and this was confirmed by showing that 

 pyruvate is formed from fructose- 1,6-diP but not from glucose or the hexose 

 monophosphates in the presence of iodoacetate. It may also be mentioned 

 that Holzer et al. (1955 b) found anaerobic glycolysis to be inhibited to the 

 same degree by iodoacetate when either glucose or fructose is the substrate 

 for ascites cells. 



These apparently discrepant results may be explained in a variety of 

 ways. Beevers (1950) determined the CO2 formation by yeast rather than 

 the appearance of ethanol, and it was previously pointed out that this is 

 not necessarily a reliable measure of fermentation or the EM pathway. 

 Possibly some of the CO2 formed after addition of fructose-l,6-diP arose 

 from hydrolysis of the compound and the consequent acidification, this 



