CYTOCHROMES 155 



length of the incident hght and observing the galvanometer deflec- 

 tions of the photoelectric device. In this way he arrived at the above 

 potential for cytochrome c. 



Perhaps more startling was his finding that all three cytochromes 

 appeared to have the same potential; that is, at a given Eh level all 

 were equally reduced. This is distinctly a contradiction of Ball's 

 finding that in a heart muscle extract the cytochrome potentials 

 diflfered markedly. In Ball's work, however, the relative degree of 

 reduction of the cytochromes was measured when in equilibrium 

 with systems of known potential and systems known to react with 

 the cytochromes, whereas in Baumberger's work the normal re- 

 ductants within a more organized structure establish the equilibrium. 

 A legitimate question concerning these experiments would be 

 whether it can be assumed that the potential recorded by a platinum 

 electrode in a yeast suspension is the same as that existing within 

 the cell. And, furthermore, is it not likely that different points in 

 the organized cells actually have very different potentials? The data 

 might indeed be taken as evidence for the latter hypothesis. Baum- 

 berger suggests the possibility of a molecular aggregate of the three 

 cytochromes which is oxidized or reduced as a whole or in which 

 the three cytochromes do have the same potential. 



In a more disorganized structure, such as a heart muscle extract, 

 these relations apparently do not exist, and it is not unlikely that 

 this explains the great difference between the frequency of oxida- 

 tion and reduction of cytochromes in the intact yeast as compared 

 with that in extracts. Certain it is that in the study of tissue respira- 

 tion the problem of adsorption and dependence of function on 

 organized structure is met most frequently in the consideration of 

 the cytochrome system (see "Oxidation and Cell Structure" in Korr, 

 30). 



Cytochrome Oxidase (Cytochrome a^).—\t may be recalled that in 

 1924 Warburg (31), upon observing the cyanide sensitivity of cellu- 

 lar respiration in conjunction with the catalytic behavior of the 

 hemin-charcoal model, gave the name Atmungsjerment to the cata- 

 lytically active iron compounds involved in cellular respiration. 

 This study continued with measurements of the inhibition of yeast 

 respiration by carbon monoxide and its reversibility by light (32, 33). 

 By measuring this effect at various light frequencies, the relative 

 carbon monoxide spectrum and later the absolute carbon monoxide 

 spectrum of the Atmungsferment were determined (34, 35). It 

 was renamed the Sauerstoffiibertragendes Ferment or oxygen- 



