342 



RIBOFLAVIN 



is based upon the fact that a mixture of hexose monophosphate, Robison 

 hexose monophosphoric enzyme (zwischenferment), and coenzyme II 

 (TPN) does not react with molecular oxygen. When the old yellow enzyme 

 is added to this mixture, the following reactions take place: 



B OH 



C 



I 

 HC— OH 



I 

 HOC— H O 



HC— OH 



I 

 HC 



OH 



+ TPN + H2O 



Triphospho- 



pyridine 



nucleotide 



z wischenf erment 



> H2TPN + 



HC— O— P=0 

 H \ 



OH 



COOH 



HC— OH 



HOC— H 



HC— OH 



HC— OH 



OH 



H2-TPN + flavoprotein -^ TPN + Ha-fiavoprotein 

 H2-Flavoprotein + O2 — ^ flavoprotein + H2O2 



H— C— O— P=0 

 H \ 



OH 



Phosphogluconic acid 



As previously stated, this cycle of oxidation and reduction is relatively 

 slow even when pure oxygen is used. 



2. Synthetic, or Crossed, Yellow Enzyme 



The property of the flavin coenzymes which makes it possible for them 

 to form complexes with foreign apoenzymes was utilized by Warburg and 

 Christian^i to make the first synthetic flavoprotein. They combined the 

 protein part of the old yellow enzyme with flavin adenine dinucleotide and 

 showed that the resulting holoenzyme could, like the old yellow enzyme, 

 catalyze the oxidation of both di- and triphosphopyridine nucleotides. How- 

 ever, the catalytic activity was even less than the slow rates shown by the 

 old yellow enzyme. 



