VITAMINS 



333 



lo be especially dependent on the utilization of carbohydrates, and 

 for that reason a thiamine deficiency is more serious in nerve tissues, 

 leading quickly to pronounced alterations in nerve function. 



RIBOFLAVIN 



Chemistry 



Riboflavin, an essential substance also called vitamin Bo, was first 

 isolated in 1879 from milk. Yet its importance was not realized until 

 after extensive studies in 1933 and 1934 showed that the compound 

 promoted the growth of rats. The accepted structure, 



OH OH OH 



CH.>- 



-C C C C H-O H 



1 I 1 

 H H H 



CH 



N^^N. 



r=0 



CH3%^\N^\/N 



H 



O 



riboflavin (vitamin B2) 



is composed of the lower isoalloxazine portion attached to the group 

 related to D-ribose and called the D-ribityl group. Although complex, 

 this molecule has been synthesized and in 1957 was available in 

 pharmaceutical grades at $40/kg. 



Riboflavin functions in the animal body in the form of prosthetic 

 groups (for proteins) called flavin mononucleotide (FMN) and flavin 

 adenine dinucleotide (FAD). The former differs from riboflavin itself 

 in having a phosphate attached to the end hydroxyl of the ribityl 

 group. Flavin adenine dinucleotide is written thus: 



CH.,- 



OH OH OH O 



111 II 



C — C — C — CHOP- 



I 

 o 



-0 



flavin adenine dinucleotide (FAD) 



It is at once apparent that the right half of this molecule is like that 

 of the coenzyme DPN+ (page 140). 



