B VITAMINS: WHAT THEY ARE 5 



coenzymes I and II, riboflavin nucleotides, and even flavoproteins, etc., 

 would be considered as vitamins because they are capable of counteract- 

 ing respectively thiamine, niacin and riboflavin deficiencies. Actually, 

 they are not designated as vitamins. The easiest way out of the difficulty 

 in a specific case is to consider as a vitamin only the simplest compound 

 capable of performing the specific nutritional function. In cases where 

 two or more compounds of about the same complexity function alike 

 nutritionally, each may conveniently be called a vitamin. Nicotinic acid 

 and nicotinamide on the one hand, and pyridoxal, pyridoxamine and 

 pyridoxine on the other, are examples. 



The importance of some of the compounds commonly designated as 

 vitamins does not rest, moreover, solely upon their functioning in nutri- 

 tion. Nicotinamide from the nutritional standpoint may not be essential 

 for animals if tryptophan is abundantly supplied, yet it is a nutritional 

 substance and is important in that it constitutes a part of the metabolic 

 machinery in every cell. Even though mammals generally, including 

 human beings, are probably capable of synthesizing nicotinamide in their 

 bodies from tryptophan, it is nonetheless a compound of great biochemical 

 interest and importance. Likewise, the importance of thiamine, riboflavin, 

 pantothenic acid and other members of the B family of vitamins does 

 not depend only upon the fact that they cannot be synthesized by higher 

 animals. As essential parts of the metabolic machinery, they are most 

 fundamental, regardless of their nutritional importance. Their nutritional 

 functioning may even be considered of secondary significance. 



Looking at the matter with these facts in mind we may suspect that 

 the B vitamins actually belong to a larger group of organic catalytic 

 units which are indispensable to all cells, but which may or may not be 

 vitamins in the nutritional sense. Some of these indispensable units may 

 be uniformly synthesized by higher animals. We have no name for this 

 inclusive group of catalytic substances,* if such exists, and it appears 

 premature to discuss them at present. Until the time arrives when we 

 fully recognize the existence of such a group, it will be well to retain the 

 term "vitamin" and the nutritional concept which underlies it. A sub- 

 stance therefore cannot be classed as a vitamin unless it functions nutri- 

 tionally for higher animals. 



Following this line of reasoning we may expand our definition of a B 

 vitamin to include those organic substances which act catalytically in 

 all living cells and which junction nutritionally for at least some of the 

 higher animals. We cannot guarantee, of course, that this delineation of 

 B vitamins will remain valid indefinitely. If it should be found that some 

 of the typical B vitamins lack a catalytic function or that some of them 



* The name "catalins" has, however, occurred to the author as an appropriate one. 



