140 



THE CELL AND PROTOPLASM 



NHa 

 Fe 



NH; 



Fe 



m 



Fe<: 



N 



Fe 



N 



Fe 



NHj. 

 I 



NH 



NH 



NH 



N 



as shown in the treatment with acid acetone 

 already mentioned. The amino residues 

 attached to the iron atom deprive the cyto- 

 chrome of the ability of forming addition 

 compounds with oxygen (or carbon mon- 

 oxide, and so on). One may ask why na- 



P rote in 



Cytochrome-c 



ture has specialized cytochrome-c in this 

 way, enabling it to perform the valency 

 change 



Fe^+ ^ Fe*+-*- + e, 

 but not the addition of oxygen. I imagine 

 the answer must be that the formation of 

 a compound Fe++ O2 would be an unfavor- 

 able property for a hemin ferment acting by 

 means of valency oscillations. We may see 

 this from a comparison with hemoglobin. 



Only hemoglobin, but not oxyhemoglobin, 

 can be oxidized to methemoglobin. Thus 

 oxygen and carbon monoxide to an even 

 greater extent have a certain tendency to 

 preserve the iron in the divalent state by 

 decreasing the concentration of the hemo- 

 globin in favor of the oxygen hemoglobin. 

 Thus, just as the formation of methemo- 

 globin is unfavorable for the special func- 

 tion of hemoglobin, the formation of an 

 oxygen compound of ferrocytochrome-c 

 would possbly mean a hindrance to its 

 function. 



Type III of the ferricytochrome, which 

 occurs at physiological pH values, is the one 

 which the iron atom best preserves against 

 complex formation with inhibiting reagents ; 

 type II forms a fluoride compound, the 

 fluoride entering into a compound with the 

 iron and thus replacing the amino group. 

 Types IV and V form CN-complexes. CO 

 complexes are formed by ferrocytochrome 

 in both acid and alkaline solutions, ON com- 

 plexes in alkaline solutions. 



In the case of cytochrome-c we thus have 

 a nice demonstration of the interaction be- 

 tween the prosthetic group and the protein 

 component, and that is how the protein can 

 greatly modify and specialize the properties 

 of the prosthetic group of a ferment. 



The catalases are ferments, occurring in 

 practically all living cells. As you all know, 

 they split hydrogen peroxide into water 

 and oxygen. Zeile and Hellstrom pro- 



