678 5. OXIDANTS 



A. tereus 0.1 mM ferrocyanide has no effect on glucose utilization but in- 

 creases the yield of itaconate, due presumably to the piling up of citrate 

 (Bentley and Thiessen, 1957). The uptake and metabolism of itaconate are 

 inhibited by ferrocyanide, which is reasonable on the basis of the inhibition 

 of isocitrate dehydrogenase, and the assumption that itaconate feeds into 

 the cycle (Shimi and Nour El Dein, 1962). There has been very little work 

 on the effects of either ferro- or ferricyanide on cycle enzymes, but it ap- 

 pears likely that ferrocyanide blocks tricarboxylate steps selectively, where- 

 as ferricyanide less potently inhibits pyruvate oxidation. More work should 

 be done on these effects since no other specific inhibitor of isocitrate dehy- 

 drogenase is known. 



A few miscellaneous observations on ferricyanide may be interpreted 

 when more is known of the basic actions. Thus, 10 mM ferricyanide inhibits 

 P^2 incorporation into phospholipids 19% while stimulating respiration 17% 

 in M. tuberculosis, in this way acting more like the uncoupling agents (azide, 

 dinitrophenol, and arsenate) than the common SH reagents (Tanaka, 1960). 

 Whereas other oxidants and SH reagents frequently cause mitochondrial 

 swelling, ferricyanide is without effect, which could scarcely be due to per- 

 meability factors (Rail et al., 1962). Porphyrin synthesis from porphobili- 

 nogen is strongly inhibited by 1 mM ferricyanide; this may be partly the 

 result of direct oxidation of the porphyrins (Rimington and Tooth, 1961). 

 The eggs of Urechis and Hemicentrotus are very sensitive to ferricyanide, 

 0.02 mM elevating the fertilization membrane in the former and causing 

 cytolysis in the latter (Isaka and Aikawa, 1963). The dorsal-ventral modifi- 

 cation i^roduced hy ferricyanide in Dendraster eggs, whereby either dorsal 

 induction or ventral inhibition is manifest, is similar to that produced by 

 iodoacetate or iodine, but is unexplainable since the factors involved in 

 bilaterality are completely unknown (Pease, 1941). The effects of ferricy- 

 anide on the naturally occurring quinones must occasionally be important. 

 For example, ferricyanide potentiates very markedly the growth-inhibiting 

 activity of menadione on yeast, due to the fact it reoxidizes the reduced 

 menadione and hence maintains the naphthoquinone in the active form 

 (Kiesow. 1960 b). 



IODINE 



Iodine has been used more frequently than the oxidants previously dis- 

 cussed for the oxidation of protein 8H groups and in enzyme studies, and 

 yet it seems under most conditions to be less specific than the others. Al- 

 though it is quite a potent inhibitor of many enzymes, unless one can de- 

 termine if a particular protein group is oxidized, or otherwise attacked, the 

 information obtained is negligible. Another complication in the use of iodine 

 is the multiplicity of forms in solution and the difficulty in characterizing 

 the nature of the oxidation reaction. 



