THE FLAVOPROTEINS 147 



agents; the reaction between Haas's new yellow enzyme or Straub's 

 yellow enzyme and oxygen is very slow, unless methylene blue is 

 used as a "carrier." Possibly carriers other than methylene blue exist 

 in respiring cells. Xanthine oxidase and aldehyde oxidase react with 

 reducing agents which, while important, do not contribute greatly 

 to the production of energy. Lipmann (33), using the Warburg 

 separation technique, split from a soluble fraction obtained from 

 Bacterium Delbriickii (Lactobacillus delbrilckii) a protein portion 

 which was active as pyruvic acid oxidase only when both thiamine 

 pyrophosphate and alloxazine adenine dinucleotide were added. 

 From this result he postulated that a yellow enzyme possibly 

 oxidizes thiamine pyrophosphate. Green, Knox, and Stumpf (34) 

 have recently reported the finding of another yellow enzyme, the 

 function of which has not yet been determined. 



Formerly it was assumed that cytochrome b, because of its poten- 

 tial, acted as one of the intermediaries between the flavoproteins and 

 cytochrome c, but the discovery of cytochrome c reductase has 

 obviated the necessity for any such intermediary, although in the 

 intact cell it may act as such (two or more paths of oxidation may be 

 in operation). 



At present nine flavoproteins are known, not all of which react 

 with both the oxidizing and the reducing agents which are present 

 in the living cell; the discovery of more or these important enzymes 

 will undoubtedly follow. The relatively large riboflavin content of 

 the liver and the kidney and the multiple and complicated bio- 

 chemical functions of these organs alone indicate that we might 

 expect to find many more members of this class of enzymes. 



REFERENCES 



1. Stern, K. G., and Holiday, E. R., Ber., 67, 1104, 1442 (1934). 



2. Warburg, O., and Christian, W., Biochem. Z., 254, 438 (1932); 263, 

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3. KuHN, R., et al, Ber., 66, 1034 (1933); 68, 1765 (1935); 69, 1557 (1936). 



4. Karrer, p., Helv. Chim. Acta, 18, 69, 72, 426 ( 1935); Ber., 68, 216 ( 1935). 



5. Theorell, H., Biochem. Z., 272, 155 (1934). 



6. KuHN, R., Rudy, H., and Weygand, F., Ber., 69, 2034 (1936). 



7. KuHN, R., and Wagner- J auregg, Th., Ber., 67, 361 (1934). 



8. Haas, E., Biochem. Z., 290, 291 (1937). 



9. Haas, E., Harrer, C, and Hogness, T. R. (unpublished). 



10. Krebs, H. a., Biochem. J., 29, 1620 (1935). 



11. Warburg, O., and Christian, W., Biochem. Z., 296, 294; 298, 150 (1938). 



12. Haas, E., Biochem. Z., 298, 378 (1938). 



13. Straub, F. B., Biochem. J., SS, ISl (1939). 



14. Warburg, O., and Christian, W., Biochem. Z., 298, 368 (1938). 



15. Ball, E. G., J. Biol. Chem., 128, 51 (1939). 



