ANAEROBIC GLYCOLYSIS AND FERMENTATIONS 61 



mitochondrial suspensions could be used. Lehninger (1949) reported that 

 iodoacetate does not uncouple phosphorylation associated with NADH oxi- 

 dation by rat liver mitochondria, and later (Lehninger, 1951) confirmed this 

 for /?-hydroxybutyrate oxidation. However, he states that iodoacetamide 

 uncouples (no data given), perhaps because it can penetrate into the mito- 

 chondria while iodoacetate cannot, which is unlikely. Kaufman (1951) also 

 found phosphorylation to be unaffected by iodoacetate during oxidation of 

 a-ketoglutarate by a pig heart preparation. No reduction in oxidative phos- 

 phorylation by iodoacetate has been reported for beef heart mitochondria 

 oxidizing NADPH (Joshi et al., 1957) or for sweet potato mitochondria 

 oxidizing citrate (Hackett et al., 1960). On the other hand, there have been 

 three reports demonstrating an uncoupling action. Phosphorylation is in- 

 hibited more than oxygen uptake in rat kidney homogenate oxidizing suc- 

 cinate (Hirade, 1952), and is inhibited 56% by 1 raM iodoacetate in rat 

 liver mitochondria oxidizing choline while oxygen uptake is unaffected 

 (Rothschild et al., 1954). The P:0 ratio of guinea pig liver mitochondria 

 oxidizing glutamate is decreased from 2.6 to 2.1 by 0.3 raM iodoacetate 

 (Chari-Bitron and Avi-Dor, 1959 b). Although endogenous mitochondrial 

 phosphorylation is inhibited 70% by 5 raM iodoacetamide (Weinbach, 1961), 

 no data on the oxygen uptake are available. 



The important problem of whether iodoacetate and iodoacetamide can 

 uncouple oxidative phosphorylation is thus still open. Although partial un- 

 coupling may be observed in certain instances, it seems safe to say that a 

 true uncoupling does not occur, i.e., that phosphorylation is not so specif- 

 ically blocked that oxygen uptake is released and increased, as occurs with 

 the classic uncouplers such as 2,4-dinitrophenol. 



ANAEROBIC GLYCOLYSIS AND FERMENTATIONS 



The most important effect of iodoacetate is to depress the formation of 

 lactate, ethanol, and other products from the breakdown of carbohydrate 

 by an inhibition of 3-PGDH. This action can usually be measured accurately 

 only under anaerobic conditions where the Embden-Meyerhof glycolytic 

 pathway is solely responsible for the metabolism of glucose and related 

 sugars. In this section we shall, therefore, consider the effects of iodoacetate 

 on this pathway under anaerobic conditions, and in the following sections 

 extend the treatment to aerobic situations in which other pathways may 

 be operative. An attempt will be made to answer the following questions. 

 (1) What is the optimal iodoacetate concentration range for the inhibition 

 of the glycolytic pathway? (2) Is the glycolytic pathway in different organ- 

 isms and tissues equally inhibitable by iodoacetate? (3) Is the site of inhi- 

 bition entirely on 3-PGDH? (4) What is the chronological sequence of 

 change brought about in cells by the action of iodoacetate? (5) Is it pos- 



