62 1. lODOACETATE AND lODOACETAMIDE 



sible to block the glycolytic pathway selectively? It is believed that these 

 are the basic problems in the use of iodoacetate and that only by under- 

 standing them can this inhibitor be properly applied. The answer to the 

 last question will have to await discussion of the effects of iodoacetate on 

 various metabolic systems (see page 167). 



There has been a good deal of confusion in the terminology and methods 

 for determination of glycolysis. In the literature one finds glycolysis meas- 

 ured by the formation of lactate, the formation or release of CO.,, the utili- 

 zation of glucose or other carbohydrate, and occasionally the formation of 

 various substances other than lactate. Anaerobic glycolysis is frequently 

 equated with Q^o, '^^ the assumption that the COo driven off from a bicar- 

 bonate medium is due to the lactic acid formed. First, the increase in acidity 

 during glycolysis is not due to the ionization of lactic acid, since at physio- 

 logical pH's the lactate anion is formed from the pyruvate anion. The over- 

 all process may be represented by 



CeHi.Oe -> 2 C3H5O3- + 2 H+ 



but the hydrogen ions arise much earlier than lactate in the pathway. Sec- 

 ond, hydrogen ions may be given off or taken up by other reactions pro- 

 ceeding in the preparation, e.g., in phosphate transfers. However, Qco, is 

 a measure of anaerobic glycolysis, whereas Qc6„' which has been termed 

 aerobic glycolysis, is by no means necessarily related to glycolysis as origi- 

 nally defined. It is preferable to determine lactate directly both aerobically 

 and anaerobically. The following terminology will be used in this book. 

 Glycolysis is the metabolism of sugars (particularly glucose) to lactate, and 

 may be either aerobic or anaerobic. Glycogenolysis is the metabolism of 

 glycogen to lactate. Fermentation is the anaerobic metabolism of any sub- 

 stance in microorganisms. The Embden-Meyerhof glycolytic pathway, which 

 will be designated the EM 'pathway, is the sequence of reactions from glu- 

 cose to pyruvate, and does not include phosphorylase, lactate dehydrogen- 

 ase, or other enzymes acting on pyruvate. This may be at slight variance 

 with previous usage, but it is felt that some term must be used to represent 

 this pathway in discussions of the effects of iodoacetate. The pentose-P path- 

 way is one of the routes of carbohydrate metabolism alternate to the EM 

 pathway and involves a direct oxidation of glucose-6-P with subsequent 

 formation of pentose-P's and triose-P. 



Sensitivity of the EM Pathway to Iodoacetate 



Results on the inhibition of anaerobic glycolysis and fermentations with 

 iodoacetate and related inhibitors in a variety of organisms are given in 

 Table 1-11. Some preparations are cellular and others acellular, different 

 methods were used, and, perhaps more important, different incubation 



