RESPIRATORY METABOLISM 375 



accumulates and in E. coU cultures can be measured experimentally. In 

 anaerobes which normally do not possess catalase, this mechanism might 

 explain the bacteriostatic effect of oxidation-reduction indicators. 



It is also known that there are certain pigments of bacteria and yeasts 

 (e.g., yellow enzyme, or pyocyanine) which are capable of bringing 

 about a similar result, and other naturally occurring oxidation-reduction 

 indicators have been described (echinochrome, hermidin, and pigments 

 from B. violaceus and Chromodoy'is zebra) which apparently might func- 

 tion in a similar fashion. The reactions involving yellow pigment and 

 its coenzyme may be indicated as follows: 



(6) substrate -f- coenzyme - oxidized substrate -\~ reduced 



dehydrogenase 



* coenzyme 



(7) reduced coenzyme -[- yellow pigment ;:± coenzyme -j- 



leuco-yellow pigment 



(8) leuco-yellow pigment -|- oxygen ^ yellow pigment -j- H2O2 



(9) H,0,^=~ H,0 + l/2 0, 



catalase 

 In this case only the action of catalase is prevented by HCN, and there- 

 fore H2O2 accumulates. In the absence of Oo the leuco-yellow enzyme 

 may be oxidized by other substances (e.g., by methylene blue). The 

 yellow enzyme has been found to be a combination of protein and 

 vitamin G, and it is believed that while this sort of system is present 

 in aerobic organisms, it assumes its greatest importance in anaerobic 

 species. In anaerobic organisms (yellow enzyme can be prepared from 

 bottom beer yeast or lactic acid bacilli) we have, then, a respiratory 

 system which is quite independent of cytochrome and Warburg's oxidase, 

 and which therefore is insensitive to HCN and CO. Perhaps when we 

 say that the respiration of a given species is cyanide insensitive, we may 

 be inferring that that species has a respiratory system more suited to 

 anaerobic conditions (temporary or otherwise). Under anaerobic condi- 

 tions the leuco-yellow pigment is probably oxidized by substances other 

 than molecular oxygen, and HgOg is not formed. The known respiratory 

 enzymes of bacteria are summarized by Frei (1935) and Stephenson 

 (1939). 



The relationships between the various respiratory enzyme systems 



