RESPIRATORY FERMENT AND RELATED CYTOCHROMES 365 



The inhibition of the respiration of different tissues raises compli- 

 cated problems which are only partly solved today. This will be 

 discussed further in Section 5.4. 



3.6.3. Cytochrome ai. Acetobader pasteurianum is a strongly re- 

 spiring organism, which may be presumed to contain a relatively large 

 concentration of respiratory ferment. For this reason it was studied 

 by Warburg and his collaborators in the hope of finding the respira- 

 tory ferment bands by direct spectroscopy. A band at 589 m/n was 

 indeed observed, which was shifted by carbon monoxide to 593 m/x, 

 approximately the position of the absorption band in the photo- 

 chemical absorption spectrum of the respiratory ferment of yeast. 

 The compound thus combines with carbon monoxide. The visible 

 spectrum of the carbon monoxide compound tallied closely with the 

 photochemical absorption spectrum of the respiratory ferment of this 

 organism (1592,2953,2955,2958), while both definitely deviated from 

 that of yeast : 



Acetobader: I, 589; II, 546; III, 524; IV, 430 mn (1592) 

 Yeast: I, 589; II, 560; III, 510; IV, 430 m^u (1908,2954) 



Keilin considered this compound a cytochrome and termed it cyto- 

 chrome ai. 



On aeration the band of ferrocytochrome ai disappears; according 

 to ^yarburg there is also spectroscopic evidence of combination with 

 cyanide. Cytochrome ai would thus appear to have all the properties 

 demanded for a respiratory ferment. 



The evidence for the combination with cyanide is, however, not clear. 

 Warburg (2953) observed a band at 639 m/x which he ascribed at first to the 

 cyanide compound of ferricytochrome ai. Later (29oo,2958), however, the 

 band was observed together with that of ferrocytochrome ai in the presence 

 of alcohol, and an involved explanation was given assuming that the (iSQ-m^ 

 band was that of the cyanide compound of another hematin compound, the 

 latter functioning as reducer of the respiratory ferment (cytochrome aO and 

 as oxidizer of cytochrome a. In contrast to Warburg, Fujita, and Kodama 

 (962) found that cyanide in the presence of air shifted the oSO-mju band 

 slightly toward the red. The band observed by the Japanese authors is, 

 however, probably the band of a ferrous cyanide compound rather than of a 

 ferric cyanide compound, since Keilin (1492,1493) has found a similar band 

 for the ferrous cyanide compound of cytochrome as. As will be discussed 

 below, the cytochrome ai of A. pasteurianum is, if not identical with, cer- 

 tainly closely related to Keilin's cytochrome as. 



Lemberg and co-workers (1698) pointed out that the formation of the 

 639-m)u band may be interpreted in another way. The cyanide may poison 



