146 1. lODOACETATE AND lODOACETAMIDE 



preparations is whether iodoacetate is blocking uptake of P^^, the actual in- 

 corporation of P^^, or some other pathway such as glycolysis, the decreased 

 formation of lipid-P^^ being only a reflection of a depression of precur- 

 sors. Thus in cat brain slices 1 mM iodoacetate inhibits 86% the formation 

 of lipid-P^2 but this could be on glycolysis rather than a specific effect on 

 phospholipid synthesis (Strickland, 1954). In Mycobacterium tuberculosis the 

 incorporation of P^^ into lipid-P^^ is depressed around 50% by 1 mM iodo- 

 acetate with fumarate and pyruvate as substrates, the O2 uptake being 

 unaffected, so that here a nonglycolytic site is likely (Tanaka, 1960). The 

 incorporation in subcellular preparations varies with the organism or tissue 

 as well as the conditions of the experiment. Thus in brain dispersions, iodo- 

 acetate inhibits weakly if pyruvate is the substrate (Dawson, 1953) but 

 very strongly if glucose is the substrate (McMurray et al., 1957 a). In the 

 latter case, iodoacetate at 0.01 mM depresses the incorporation into phos- 

 pholipid 40% aerobically and 72% anaerobically. There are two systems 

 for the synthesis of phospholipids, one dependent on glycolysis and the 

 other on the cycle in mitochondria (McMurray et al., 1957 b), and the latter 

 is not inhibited by 0.01 mM iodoacetate. Little work on the incorporation 

 of phosphorylated intermediates has been done but, in rat brain extracts, 

 1 mM iodoacetate inhibits choline-P^^ -^ lipid-P^^ 590/^ ^^^^ a-glycerol-P^^ 

 -^ Hpid-P32 96% (McMurray et al, 1957 c). The incorporation of acetate- 

 1-C^* into phospholipids in liver slices is completely blocked by 1 mM iodo- 

 acetate (KHne and DeLuca, 1956). Although the evidence is not complete, 

 it is reasonable that iodoacetate can exert some direct effect on the later 

 steps in the synthesis of phospholipids, but in other instances the action is 

 mainly through glycolytic depression. In the biosynthesis of lecithin, how- 

 ever, the formation of choline is not sensitive to iodoacetate (Bremer and 

 Greenberg, 1961). 



EFFECTS ON PROTEIN AND AMINO ACID METABOLISM 



The effects of iodoacetate on proteolytic enzymes have been discussed 

 (page 39) and it is evident that certain intracellular cathepsins and pro- 

 teinases are quite sensitive while others are very resistant. Some may well 

 be as sensitive as 3-PGDH and, particularly in experiments involving the 

 nutrition and growth of microorganisms, these effects must be taken into 

 account. There is presumably a balance between protein synthesis and 

 breakdown, and this may be disturbed by iodoacetate in either direction 

 since, as we shall see, protein formation is quite sensitive to iodoacetate. 



Ammonia formation and release from tissues interested the early work- 

 ers, inasmuch as to most they appeared to reflect protein or amino acid 

 catabolism. It is now known that ammonia can arise from a number of 

 reactions: the reduction of nitrate and nitrite, the deamidation of glutamine 



