376 VIII. HEMATIN ENZYMES, I. CYTOCHROME SYSTEM 



the reaction are formed by autoxidation of adrenaline or ascorbic acid, while 

 later more hydrogen peroxide is supplied by autoxidation of the reductant 

 of the quinoid system. The system is thus a pseudo-oxidase. 



Ames and Elvehjem (^6, cf. also 259,3178a) described a glutathione oxida- 

 tion by mouse kidney which required cytochrome c. The system was inhibited 

 by diethyldithiocarbamate (a specific copper inhibitor), not by azide, and 

 more stringent evidence is required before it can be accepted that cytochrome 

 oxidase plays a role in it. These reactions resemble the coupled oxidation of 

 hemoglobin (and other hematin compounds) with ascorbic acid and other 

 hydrogen donors; they are probably of no significance in biological respiration, 

 since they are accompanied by a destruction of the hematin catalyst {cf. 

 Chapter X). 



The stepivise lowering of the oxidation-reduction potential. Table V, taken 

 from a paper of Ball {l2Jt), shows that the arrangement oxidase -cytochrome 

 a-cytochrome c-cytochrome b postulated above for the complete systemisin 

 agreement with the oxidation-reduction potentials found for the different 

 cytochromes and that about two-thirds of the total energy obtainable by 

 the oxidation of substrate is released in the steps involving the cytochrome 

 system. 



TABLE V 



Oxidation-Reduction Potentials" in Cell Respiration 



Ej System 



-h 0.81 Oxygen 



? Cytochrome oxidase 



-f- 0.29 Cytochrome a 



+ 0.25 Cytochrome c 



0.00 Succinate, fumarate 



— 0.05 Cytochrome b 



— 0.07 Flavoprotein 



— 0.30 Pyridine nucleotide; substrate dehydrogenases* 



— 0.41 Hydrogen 



" According to Ball {12 Ji). 



^ The potential of these systems varies from 0.00 to —0.41. 



The stepwise lowering of the oxidation-reduction potential with specific 

 interaction of several .systems not greatly different in potential is probably 

 required for the complete topochemical correlation of all the processes in the 

 cell. If this correlation is disturbed, damage to the cell ensues. Respiration 

 of sea urchin eggs, for example, is stimulated by very low concentrations of 

 nitrophenols and other substituted phenols, but cell development and cell 

 divisions are stopped, although the increased respiration is catalyzed by the 

 cytochrome .system {cf. 2017, p. .566, 570 ff.). 



Dimethyl-p-phenylenediamine acts probably differently in so far as it 

 replaces the normal substrates, while the phenols are considered carriers 

 between the cytochromes and the normal substrate sy.stems, but the effect 

 is the same. It is interesting tliat this amine produces liver tumors and that 



