82 1. lODOACETATE AND lODOACETAMIDE 



early observation of Ehrenfest (1932) that 0.1 niM iodoacetate inhibits yeast 

 fermentation completely at pH 4.6 if added some time before glucose, where- 

 as when both iodoacetate and glucose are added together the inhibition 

 develops very slowly. 



Patterns of Anaerobic Glucose Utilization in the Presence of Iodoacetate 



Even though the EM pathway is blocked at 3-PGDH, glucose may still 

 be metabolized to a certain extent if ATP is available. We have seen that 

 hexose phosphates may be formed and accumulate during iodoacetate block. 

 In the anaerobic experiments of Stickland (1956 b) with yeast, of a total of 

 1.50 mg/ vessel of glucose utilized, 1.07 was fermented, 0.24 went to poly- 

 saccharide, and 0.19 was unaccounted for. In the presence of 0.25 mM iodo- 

 acetate, 0.21 mg/ vessel of glucose was utilized, 0.07 being fermented and 

 none going to polysaccharide, leaving 0.14 unaccounted for. There is thus 

 a strong inhibition of polysaccharide synthesis in yeast, as well as a 93% 

 block of fermentation. The unaccounted for fraction may be hexose phos- 

 phates, but it appears likely that ATP is reduced to levels not supporting 

 active phosphorylation, unless there is some inhibition of the pathway for 

 polysaccharide synthesis. 



A greater discrepancy between inhibition of anaerobic glycolysis and glu- 

 cose uptake is seen in duck erythrocytes (Tosteson and Johnson, 1957). 

 Iodoacetate at 1 mM reduces lactate formation from 2.6 to 0.1 millimole/ 

 liter of RBC/hr, but depresses glucose uptake only from 2 to 1 millimole/ 

 liter of RBC/hr, indicating that it is being metabolized. Since it is unlikely 

 that glycogen formation can account for the glucose taken up, one is left 

 with the alternative generation of hexose phosphates. One wonders also 

 how much glucose taken up could be accounted for by a rise in intracellular 

 glucose concentration, as has been shown to occur in other cells (see page 

 136). In lymphatic cells and lymphosarcoma, the inhibitions of glucose up- 

 take and lactate formation anaerobically are not greatly different; if any- 

 thing, glucose utilization is inhibited slightly more (Villavicencio and Bar- 

 ron, 1957). 



Summarizing this meager evidence, it appears that glucose has a very 

 limited metabolism when 3-PGDII is blocked, and that phosphorylation to 

 an extent determined by ATP supply is the primary pathway. However, 

 one must remember that Stickland (1956 b) found 67% of the glucose uti- 

 lized unaccounted for, and we are ignorant of the products of this meta- 

 bolism. 



Changes in pH during Iodoacetate Inhibition 



Anaerobic glycolysis usually leads to a decrease in the pH due to meta- 

 bolically produced protons: 



Glucose + 2 ADP + 2 P^ -> 2 lactate- -f 2 ATP -f 2 H+ 



