COENZYMES DERIVED FROM B VITAMINS 205 



instance cannot be easily correlated with any other known function of 

 folic acid. It may have some relationship to the role of folic acid in the 

 oxidation of tyrosine. 304 



Coenzymes Derived From Vitamin Bi 2 



Vitamin Bi 2 and chemically related substances have only recently 

 become available to investigators interested in studying the chemical 

 functions of these compounds. As a result, their enzymatic role has not 

 yet been clearly denned. On the basis of preliminary and incomplete 

 reports, however, it would appear that the cobalt-containing compounds 

 effective in the treatment of pernicious anemia should be added to the 

 list of factors necessary for important reactions of general biological 

 occurrence. The inclusion of the Bi 2 group in the list of B vitamins thus 

 seems warranted, not only from the standpoint of its distribution and 

 nutritional importance, but also on the basis of its function. 



Until the end of 1948, all available preparations used clinically and 

 for research were concentrated by procedures which had beeen developed 

 using clinical responses as the method of assay. Consequently, it is not 

 surprising that, in addition to the cobalt-containing factors, these crude 

 concentrates contain appreciable amounts of thymidine and other des- 

 oxyribosides which possess "vitamin Bi 2 " activity under some conditions 

 (p. 206) . The presence of these nucleosides may be desirable from the 

 standpoint of the effectiveness of the product, but it makes it impossible 

 to interpret accurately the results of experiments in which "injectable 

 liver concentrates," "purified antipernicious anemia preparations," "re- 

 fined liver extracts," etc. were used as sources of vitamin Bi 2 . 



It is impossible as yet to make any statement concerning the chemical 

 relationship of the substances possessing vitamin B i2 activity to the 

 coenzyme (s) derived from them. Two cobalt-containing compounds which 

 are therapeutically active in the treatment of pernicious anemia have 

 been reported by English investigators. 313 Both these compounds satisfy 

 the nutritional requirements of a microorganism when tested under con- 

 ditions where "vitamin Bi 2 " is essential. 314 They can be most easily 

 characterized by the rate at which they travel during chromatographic 

 separation. The slower-moving compound, presumably the more complex 

 of the two, predominates in fresh liver tissue. During autolysis, however, 

 this form of the vitamin is apparently converted enzymatically to the 

 faster-moving compound. 315 Crystalline substances independently isolated 

 in the United States to which the names vitamin B i2 316 and erythrotin 317 

 have been given are believed to be identical with the faster-moving com- 

 ponent. 



