B VITAMINS: WHAT THEY ARE 9 



Folic Acid. The vitamin activity which characterizes this substance 

 most clearly is its ability to prevent a specific type of anemia in chicks. 

 No other naturally occurring structure (except its conjugates) is known 

 to be capable of performing this function. 



OH 

 I H H 



C N C=C 



N C C-CH 2 -NH-C C-C-NH-CH-CHr-CHj-COOH 



NH 2 -C C CH C— C O COOH 



\ / \ / H H 



N N 



Folic acid (Pteroylglutamic acid) 



More complicated structures occur naturally and their physiological 

 significance will be discussed in later chapters, but the simplest com- 

 pound capable of performing the vitamin function is the one pictured 

 above, and in accordance with our previous discussion it is the only one 

 which will be considered as a B vitamin. There is no serious doubt, on 

 the basis of microbiological evidence, but that it functions universally 

 in living matter. The fact that it is effective in very minute amounts 

 strongly suggests a catalytic role. 



A series of articles dealing with the chemistry of folic acid and its 

 derivatives treat this subject rather fully. 14, 15 ' 16, 17, 18, 19 



Structurally Known Compounds of Somewhat Doubtful Status 



In addition to the seven chemically characterized vitamins with dis- 

 tinct nutritional functions listed above, there are three other well recog- 

 nized compounds of nutritional signficance: inositol, choline, and 

 p-aminobenzoic acid, which merit consideration because they possess at 

 least some of the characteristics of B vitamins. 



We have used three criteria in our previous discussions. To belong in 

 the B group a compound must: (1) function nutritionally for higher 

 animals, (2) be universally present in living cells, and (3) act or be 

 presumed to act catalytically. These criteria are listed, in our opinion, 

 in the approximate order of their importance. The status of each of the 

 three substances mentioned above can be questioned on the basis of at 

 least one of these criteria. 



Inositol appears to function nutritionally for various experimental 

 animals (though contrary evidence has been obtained 20 ), and evidence 

 for its universal occurrence is perhaps as good as for other members of 

 the group, but its relative abundance in tissues and its occurrence as a 

 structural unit in recently discovered lipides, makes one question its 

 inclusion. It is not uncommon for inositol to be present in tissues in 



