CYTOCHROMES 171 



dase under-saturated) cyanide does produce an inhibition of hydro- 

 quinone oxidation. But if the cytochromes are chiefly in the oxidized 

 state, as they are in the resting tissue, such a decrease in oxygen 

 consumption could be compensated for by increased reduction of 

 the cytochromes. It is therefore important to know whether in the 

 experiments of Stannard and of Korr azide does or does not pro- 

 duce an increased state of reduction of the cytochromes in the 

 resting tissue. 



The differences between the characteristics of the respiration of 

 the eggs of various species before and after fertihzation have been 

 extensively studied and have been related to the function of the 

 cytochrome system. The results are at present very difficult to inter- 

 pret, largely because of the tests employed for detecting the oxidase 

 or the cytochrome and because of the problem of permeability of 

 the cells to inhibitors. For example, it appears that in the un- 

 fertilized eggs of the sea urchin cytochrome has never been ob- 

 served spectroscopically, and its respiration is not inhibited by 

 cyanide or azide. After fertilization, however, the respiration is 

 typical of one proceeding through the cytochrome system (see Sha- 

 piro, 88). Korr believes the respiration of the unfertilized sea urchin 

 egg to be another case of functional inactivity of the cytochrome 

 system, since these eggs can oxidize p-phenylenediamine (see Dis- 

 cussion in Shapiro, 88). Allen (89), on the other hand, using grass- 

 hopper eggs, has shown that the activity metabolism is definitely 

 connected with the new development, rather than with "gearing," 

 of the cytochrome system. 



A recent paper by Krahl, Keltch, Neubeck, and Clowes (90) on 

 the cytochrome system of sea urchin eggs demonstrates that there is 

 a complete absence of cytochrome c in the unfertilized eggs, but no 

 lack of cytochrome oxidase. On the other hand, even in the fertilized 

 eggs, which are relatively more cyanide- and azide-sensitive, they 

 were still unable to detect any cytochrome c. The establishment of 

 the presence of cytochrome oxidase in the unfertilized eggs, al- 

 though it does not constitute proof, is strong evidence that this com- 

 pound functions in the respiration of these cells. The authors favor 

 the hypothesis suggested earlier (91) and described by Ball (page 

 29) that the action of cyanide and azide on cellular respiration may 

 be related to the formation of a complex with the oxidase possessing 

 a lower potential than the original oxidase (92, 93). The sensitivity or 

 stability of a respiration to azide or cyanide then depends on the 

 potential of the oxidase-inhibitor complex formed and the potentials 



