660 5. OXIDANTS 



(Ghosh, 1958), at 1 mM inhibits green gram flavokinase 48% (Giri et at., 

 1958), at 0.1 mM inhibits /?-fructofuranosidase 94% (Sizer, 1942 a), at 

 10 mM inhibits /5-glycerophosphatase 100% (Rao et al, 1960), at 2 mM 

 inhibits Aerobacillus hydrogenlyase 23% (Crewther, 1953), at 0.01 mM in- 

 hibits intestinal phosphatase 95% (Sizer, 1942 b), at 1 mM inhibits Pseudo- 

 monas proteinase 100% (Morihara, 1963), and at 0.1 and 1 mM inhibits 

 beef liver urocanase 13% and 87%, respectively (Feinberg and Greenberg, 

 1959). Since these experiments were done at different pH's, temperatures, 

 and incubation times, it is difficult to compare the results accurately. In- 

 deed, no thorough investigation of the effects of pH or temperature on such 

 oxidations has been made. The moderate inhibition (12%) of liver arginase 

 by 5 mM permanganate was believed due to an effect on the Mn++ cofactor 

 rather than on the enzyme (Greenberg et al., 1956). Although yeast /?-fruc- 

 tofuranosidase is so sensitive to permanganate, it is inhibited only 16% by 

 10 mM dichromate (Sizer, 1942 a) and only 43% after 90 min incubation 

 with 123 mM periodate (Myrback, 1957 b). Dichromate is also less effective 

 than permanganate on /5-glycerophosphatase (Rao et al., 1960) and /?-amyl- 

 ase (Ghosh, 1958). In this connection, it must be remembered that the prod- 

 ucts of the reduction of the oxidant may also be inhibitory, e.g., the MnOg 

 or Mn++ from permanganate. The results of Taylor and Gale (1945) on E. 

 coli amino acid decarboxylases are interesting in that the effects of perman- 

 ganate were found to depend on the substrate used. For example, 0.1 mM 

 permanganate inhibits the decarboxylation of histidine 15%, arginine 17%, 

 glutamate 41%, ornithine 98%, lysine 100%, and tyrosine 100%. Whether 

 there are different enzymes or different effects with the various substrates 

 is not known. Permanganate and other strong oxidants can occasionally 

 act on substrates or other components of the reaction. This is illustrated in 

 the effects of permanganate and p-benzoquinone on the growth of Fusarium 

 conidia (Braune, 1963). Both are inhibitory alone but when present together 

 nullify each other and may actually stimulate growth. This was shown 

 not to be due to some oxidation product of jo-benzoquinone or reduction 

 product of permanganate. The formation was postulated of a substance X 

 which protects against p-benzoquinone and heavy metal ions. Indeed, treat- 

 ment of maleate or tartrate with permanganate gives rise to substance X. 

 Although such effects in cellular systems are complex, related actions must 

 be expected in certain enzyme systems. 



Results with nitrous acid are difficult to interpret, but in all cases the 

 inhibition progresses very slowly (Myrback, 1926). Whereas the of-amylase 

 from B. suhtilis cannot be reactivated by HgS after inhibition by nitrite 

 (Di Carlo and Redfern, 1947), the /9-amylase of barley is completely reac- 

 tivated (Weill and Caldwell, 1945 a). In the former case it was concluded 

 that SH groups are not involved in the inhibition, and in the latter case 

 that they are. Similarly, inhibitions by redox dyes may or may not be at- 



