EFFECTS ON PROTEIN AND AMINO ACID METABOLISM 147 



and asparagine, and the deamination of urea, amino acids, hexosamines, 

 nucleotides, nucleosides, and amino purines. The results are thus not easy 

 to interpret. Embden (1930; Embden and Norpoth, 1931) associated ammo- 

 nia formation with the contracture induced by bromoacetate in frog mus- 

 cles, since the ammonia content increases markedly in stimulated bromo- 

 acetate-treated muscles but not in those merely stimulated or incubated 

 with bromoacetate. Similar results were obtained by Mozolowski et al. (1931 ) 

 who showed that ammonia formation occurs maximally, not when the 

 muscle is most active but when it begins to fail and go into rigor, at the 

 time creatine-P has dropped to a low level. In mammalian tissues the si- 

 tuation seems to be different, in that Barker et al. (1939) obtained only 

 inhibition of ammonia formation, this being especially marked in brain, 

 which has a high ammonia production, 0.054 mM iodoacetate inhibiting 

 83%. Weil-Malherbe and Green (1955 a) did not find such potent inhibi- 

 tion in guinea pig brain, but observed that ammonia formation is sup- 

 pressed by glucose due to synthesis of amides. This then introduces another 

 aspect into the problem: if glucose is forming C3 and C4 acids through the 

 EM pathway and these acids are involved in the uptake of what ammonia 

 is formed, inhibition of the EM pathway would increase the free ammonia, 

 as Embden observed. However, it does not correlate with the effects in brain, 

 where ammonia formation is depressed by inhibitors of electron transport, 

 uncouplers of oxidative phosphorylation, and anoxia. Weil-Malherbe and 

 Green felt that the ammonia arises mainly in reactions associated with 

 proteolysis. Takagaki et al. (1957) clarified the picture somewhat by show- 

 ing that brain slices endogenously form ammonia with a simultaneous de- 

 crease in glutamate, more than half the endogenous respiration being ac- 

 counted for by the glutamate disappearance, which glucose inhibits. Iodo- 

 acetate at 0.05 mM inhibits 13% the endogenous ammonia formation, and 

 this is likely to be on the enzyme oxidatively deaminating glutamate. 



Essentially nothing is known of the effects of iodoacetate on the various 

 long synthetic pathways for amino acids, but certain simple reactions have 

 been studied. If guinea pig brain slices are incubated with glucose-C^*, some 

 of the label appears in amino acids, of which glutamate is the most impor- 

 tant (Tsukada et al., 1958). Iodoacetate at 0.1 mM completely inhibits 

 this, but of course the action here could be entirely on the glycolytic path- 

 way. The formation of alanine from ammonia and pyruvate in Bacillus 

 suhtilis (Fairhurst et al., 1956) and liver mitochondria (Berezovskaya, 1960) 

 is also rather potently inhibited. 



The synthesis of protein requires not only the necessary amino acids 

 (either synthesized or transported into the cell) but a source of ATP; it 

 is, therefore, quite susceptible to inhibition by iodoacetate. The transport 

 of amino acids into the cell is often reduced by iodoacetate, so this must be 

 one of the major sites for the reduction of over-all protein synthesis. The 



