VITAMINS 



233 



enzymes" because of the color imparted to them by the flavin group, 

 have the function of catalyzing the removal of hydrogen atoms from 

 certain metabolites and passing the hydrogen to some acceptor, such as 

 cytochrome c or molecular oxygen. Xanthine oxidase, d- and L-amino 

 acid oxidases, and cytochrome c reductase are examples of flavoproteins. 

 As a result of its participation in the make-up of these enzymes, ribo- 

 flavin fulfills a vital role on the "main line" of the oxidation processes 

 by which food energy is made available to living tissues. Like the other 

 B vitamins, it apparently is needed by all living cells. 



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Courtesy ol' Meixk & Co., lac. 



Fig. 9-7. Riboflavin. 



Chemical nature 



Riboflavin, which previously has also been called vitamin B2 or vitamin 

 G, is a water-soluble pigment widely distributed in plant and animal 

 materials, although in very minute concentrations. Dilute solutions of 

 it have a greenish yellow color and in ultraviolet light show a charac- 

 teristic greenish yellow fluorescence. It is, for example, the substance 

 mainly responsible for the rather faint but distinct color of whey and 

 of egg white It was first obtained in the pure state in 1933 and was 

 synthesized in 1935. The pure vitamin, which is an orange-red powder, 

 is now readily available It is produced mainly by fermentation with 

 special riboflavin-producing microorganisms, for example, Eremothedum 

 ashbyii. 



