B VITAMINS: WHAT THEY ARE 15 



extends further the list of B vitamins for the elucidation of which micro- 

 biological investigations have proved most valuable. It is also worthy of 

 note that every vitamin isolated or concentrated by using microbiological 

 tests has fallen into the category of "B vitamins" by common consent and 

 on the basis of the criteria which we have outlined (p. 5). 



Thymidine is worthy of note in this connection because of its functional 

 relation to the anti-pernicious anemia vitamin 31 and the fact that in 

 relatively large doses it is able to replace the vitamin in microbiological 

 tests. 32 Other desoxyribosides also function in a similar manner. 



HN-C=0 



0=C C— CH 3 



I 1 



ch 2 oh— ch— ch— ch 2 — ch— n— ch 

 Ah 



Thymidine 



The interrelationship between thymidine and the pernicious anemia 

 vitamin will be discussed in a later section (p. 474). 



Strepogenin. This growth principle was originally found in liver and 

 was effective for certain hemolytic streptococci. 33 Subsequently it was 

 found to be more abundant in certain purified proteins, notably insulin 

 and trypsinogen, and to be released most effectively by tryptic digestion. 34 

 A convenient test organism which is in current use is L. casei. 35 What 

 appears to be the same substance is also effective in promoting the growth 

 of mice. 36, 37 The available evidence indicates that the substance is of 

 peptide nature and predominantly acidic, and one synthetic peptide, seryl 

 glycyl glutamic acid, has been found to have appreciable strepogenin 

 activity. 



If strepogenin is a peptide of known amino acids without any novel 

 feature in its structure, it could hardly be classified as a B vitamin. The 

 growth principle as tested for in the usual way has not been obtained 

 in a form such that a minute amount is effective, so a catalytic function 

 for strepogenin cannot be taken for granted. It is an important nutritional 

 principle, however, and it is discussed briefly here because, pending the 

 complete elucidation of its chemical nature, it is a potential member of 

 the B vitamin family. Recently, Chattaway et al., using diphtheria or- 

 ganisms for testing, obtained a highly potent preparation from yeast 

 which is suggestive of strepogenin. 38 It is reported to possess activity by 

 virtue of the presence of two peptides and a fraction which is stable to 

 acid hydrolysis, all three of which entities are required for maximum 

 growth. 



