142 



THE BIOCHEMISTRY OF B VITAMINS 



equally important function for the riboflavin coenzymes was also early 

 appreciated — that of being the initial acceptor for hydrogen atoms in a 

 number of metabolically important dehydrogenations of aldehydes, amino 

 acids, and purines. 



When the yellow enzyme was discovered, it was realized that the yellow 

 pigment possessed the characteristics of a "flavin," a class of biological 

 pigments observed as early as 1879. 56 In 1933, riboflavin was isolated in 

 crystalline form and shown to possess vitamin activity for the rat. 57 At 

 first, it was assumed that riboflavin itself was the chromophoric com- 



Riboflavin phosphate 



CH 



Flavin adenine dinucleotide 



