670 5. OXIDANTS 



rent is unaffected (Eubank et al., 1962). Porphyrindin injected at a dose of 

 200 mg in a pregnant mouse produced neuroblastic necrosis in the fetus, 

 but not as much as p-chloromercuribenzoate, oxophenarsine, or o-iodosoben- 

 zoate, these damaging neuroblasts in a pattern similar to radiation (Hicks, 

 1953). SH reagents usually cause blebbing of Sarcoma 37 ascites cells. Por- 

 phyrindin has no effect at 2 nxM but produces symmetrical blebs at 8 roM 

 (Belkin and Hardy, 1961). Such blebbing involves a raising of the entire cell 

 membrane and presumably is due to some disturbance in water transport. 



FERRICYANIDE 



Ferricyanide has been used widely as a fairly specific oxidant for the de- 

 termination of protein SH groups. Furthermore, it is commonly used as an 

 electron acceptor in various dehydrogenase systems, since it is reduced by 

 some of the components in electron transport before cytochrome c, and fer- 

 rocyanide has often served as an electron donor in studying the cytochrome 

 system. When ferricyanide or ferrocyanide is used for such purposes, it is 

 important to consider the possibility of inhibition of the enzymes involved, 

 particularly the dehydrogenases, and to use as low concentrations as pos- 

 sible. The first use of ferricyanide for the determination of SH groups was 

 by Flatow (1928) and this was simplified by Mason (1930) so that the ferro- 

 cyanide formed could be colorimetrically estimated after transformation to 

 Prussian blue, this being suggested by Folin's ferricyanide method for blood 

 glucose. This reaction has been used for the histochemical localization of SH 

 groups but is not very satisfactory. Anson and Mirsky (1931) noted that 

 hemoglobin treated with ferricyanide yields a globin that no longer reacts 

 with nitroprusside, but it remained for Schiiler (1932) to show that ferri- 

 cyanide oxidizes more than the heme group and that globin itself reacts 

 after separation from heme. Mirsky and Anson during the next 10 years 

 elucidated the nature of the reactions between ferricyanide and proteins, 

 and applied their results to determination of protein SH groups. 



Chemistry 

 The oxidation of thiols may be written as: 



2 Fe{CN),^- + 2 R— SH ±^ 2 Fe(CN)6''- + R— S— S— R + 2 H+ 



When the SH groups are on different molecules, the kinetics are complex 

 and the detailed mechanism of the reaction is not understood. The ferro- 

 cyanide formed is usually determined by addition of Fe+++, forming Prus- 

 sian blue, but in work with proteins it is advisable to determine also the 

 disappearance of SH groups with nitroprusside or ??-chloromercuribenzoate, 

 since groups other than SH may be oxidized. The oxidation-reduction po- 



