362 VIII. HEMATIN ENZYMES, I. CYTOCHROME SYSTEM 



3.6. The Respiratory Ferment and Cytochromes Related to It 



3.6.1. The Respiratory Ferment. Shortly after the spectroscopic 

 rediscovery of the cell hemochromes by Keilin, Warburg found evi- 

 dence for the fundamental role played by a hematin compound in 

 cell respiration. The idea that iron in some form was connected with 

 cell respiration is very old. As early as 1843 von Liebig assumed that 

 hemoglobin was the respiratory ferment, a theory which soon had to 

 be abandoned. Inorganic iron was known to catalyze the autoxida- 

 tion of cysteine and to be a peroxidative catalyst. After a series of 

 model investigations by which he became convinced of the importance 

 of heavy metal catalysis for the oxidation of biological substances, 

 Warburg began the systematic study of the effect of inhibitors on the 

 respiration of wild yeast {Torula) and other cells. He found it to be 

 inhibited by cyanide (2917,2918,2920) and by carbon monoxide 

 (2919) in the dark. Irradiation with light decreased the carbon 

 monoxide inhibition. This was developed into an ingenious method 

 for measuring the absorption spectrum of the carbon monoxide com- 

 pound of the respiratory ferment {1592,2920-2922,29^6-2950), the 

 principle of which has been discussed in Chapter II. For reviews of 

 these investigations see references 292J^, 2928, and 2930. 



Photochemical Absorption Spectrum of the Respiratory Ferment. In 

 yeast and Acetobacter pasteurianum the following photochemical 

 absorption spectrum was thus found: a very high (Soret) band at 

 432-433 lUfx (€„,.M = 156), a strong band at 283 m^ {e^^i = 87), 

 and a fainter baud at 590-593 m/x (e^M = 13.5). There are also 

 weak bands in the green which appear to be different for yeast and 

 Acetobacter (cf. Section 3.6.3.). This absorption spectrum is very 

 similar to that of carbon monoxide Spirographis hemoglobin, a hybrid 

 hemoprotein synthesized from Spirographis hematin and globin (I, 

 594; II, 550 (weak); III, 434 m/x, while that of carbon monoxide 

 chlorocruorin, the naturally occurring hemoprotein, shows somewhat 

 wider differences (I, 600; II, 552; III, 439 mju) (2954). The band at 

 about 280 m/x is also found in carbon monoxide chlorocruorin, but not 

 in carbon monoxide Spirographis hemoglobin. It is therefore unlikely 

 that this band is due to the carbonyl group in the prosthetic group. 

 While the position of the main band in the violet can be fairly accu- 

 rately established by the photochemical method, this is unfortunately 

 not so for the weak bands in the visible part of the spectrum. The 



