10 THE BIOCHEMISTRY OF B VITAMINS 



amounts 100 or even 1000 times that of the more typical B vitamins. 

 Favoring the inclusion of inositol as a member of the group is the finding 

 that it constitutes a functioning portion of pancreatic amylase. 21 * This 

 indicates a catalytic role. It may be that inositol does indeed act cat- 



OH OH 



alytically like the other B vitamins and that its relative abundance is 

 explained by the fact that it also is a constituent of certain widely 

 occurring lipides. 



The relatively recent determination of the configuration of inositol is 

 alluded to in a later chapter (p. 18) . 



Choline is without question of great nutritional importance and has 

 some of the earmarks of a B vitamin. If any one of a number of mammals 

 and fowls is fed a diet deliberately made up so as to be low in choline 

 content, a serious deficiency results which can be counteracted by the 

 addition of pure choline salts to the diet. However, methionine and 

 CH 3 

 H 3 C— N + — CH 2 — CH 2 OH 

 CH 3 Cl- 

 Choline chloride 

 betaine (as well as other substances which do not occur naturally) are 

 also effective under these conditions, and it is clear that they may per- 

 form at least part of the function of choline. It appears likely that they 

 may replace choline entirely, especially in the presence of some other 

 unidentified substance. 22 Ethanolamine can evidently be methylated by 

 Type III pneumococcus 23 to produce choline which in combined form 

 (phospholipides) is probably always present in living cells. Furthermore, 

 evidence involving mutant strains of Neurospora shows clearly that the 

 synthesis of choline takes place through the intermediate formation of 

 ethanolamine. 24 



It appears clear that the naturally occurring substances, choline, betaine 

 and methionine alike, are able to furnish animals with transferable 

 methyl groups which are essential to life, and that in addition choline 



* Contradictory evidence has been reported. 21 " 



