STUDY OF RESPIRATION BY INHIBITORS 379 



ularly cytochrome c appear to be decreased. In tissues with normally high 

 cytochrome c content neoplasms occur far less frequently than in those poor 

 in cytochrome c. Not all tumors, howev^er, lack cytochrome c (Rosenthal 

 and Drabkin, 2335; cf. also the discussion remarks of Stern and Ball, 2075), 

 and while many authors {cf. above) reported a disproportion between cyto- 

 chrome oxidase and cytochrome c in tumor tissue. Potter states that in 

 general both are present in roughly proportional concentration. 



Our knowledge of the cytochrome system in invertebrates is scanty. The 

 spectroscopic observations in insect muscles have been mentioned; observa- 

 tions on the occurrence of cytochromes in other invertebrates have been 

 reported by Ball and Meyerhof (125). The "actiniohematin" of MacMunn 

 {1833) has been reinvestigated by Roche {230 Ji), who found it to consist of 

 a mixture of the cytochromes ai, bi, and c, with bi prevailing. 



5.3.2. The Cytochrome System of Plants. The distribution of the cyto- 

 chrome system in plants has been recently reviewed by James {14-09). The 

 presence of cytochrome oxidase in germinating seeds has been established by 

 Hill and Bhagvat {255,1281). The rate of oxidation of succinate was increased 

 by the addition of cytochrome c. These investigations confirm the earlier 

 observations of Keilin that plant cells contain the normal a, b, c cytochromes, 

 though in much smaller concentration than yeast, and hence difficult to 

 observe spectroscopically. Cytochrome c has been isolated from plants 

 {cf. Section 3.3.1.). Possibly the concentration of cytochrome c is lower 

 than that of cytochromes b. Thus Roche {2307) observed only the cyto- 

 chromes ai and bi in the onion; cytochromes b, not a and c, were also observed 

 in tea and carrot leaves {5Jt8,137 4,1635,187 2) and in the flavedo (white part) 

 of the orange {1374)\ cf. also the cytochrome f of Hill {1280a). 



The occurence of the cytochrome system is also indicated by observations 

 on its role in the "salt respiration" {cf. Section 5.5.) and by certain inhibition 

 experiments (Section 5.4.). Nevertheless it is not yet certain whether all 

 plants contain the cytochrome system {cf. 1409). In this regard it is of 

 interest that by growing yeast in cyanide solution a strain can be produced 

 which lacks cytochrome oxidase (Pett, 2140: Stier and Castor, 2668). 



The distribution of cytochromes in bacteria has been discussed under 

 Section 3.2. {cf. Table I; V- also 2736). 



5.4. Study of Respiration by Inhibitors 



The cytochrome system is inhibited by cyanide, azide, and carbon 

 monoxide. If the presence of other enzymes sensitiv^e to these inhib- 

 itors can be reasonably excluded, one may study the relative propor- 

 tion of respiration catalyzed by the cytochrome system by measuring 

 the degree of inhibition. It was assumed that the respiratory ferment 

 would behave in all cells in the same manner toward the inhibitors, 

 provided it was saturated with substrate. 



It could indeed be established that the respiration of some cells 

 behaved as if it were entirely catalyzed by the respiratory ferment. 



