206. THE BIOCHEMISTRY OF B VITAMINS 



The ultraviolet absorption spectrum of a crystalline preparation isolated 

 by a fourth laboratory indicates that the vitamin is "porphyrin-like." 318 

 One of the cobalt compounds already identified may be an intact co- 

 enzyme if the constitution of the prosthetic group of the B i2 enzymes is 

 no more complex than the porphyrin groups of the iron and copper 

 porphyrin enzymes. 



The reactions taking place during the biosynthesis, digestion, absorp- 

 tion, and utilization of this vitamin group are still obscure, and its 

 relationship to the "intrinsic" and "extrinsic" factors has yet to be 

 explained. A vitamin B i2 preparation was found to be inactive (when 

 administered orally to pernicious anemia patients) unless it had been 

 previously incubated with normal gastric juice. 319 Another interesting 

 fact which further clouds the picture is that the anemias in cattle result- 

 ing from cobalt deficiency can be corrected only by the oral administra- 

 tion of cobalt; parenteral injection of the ion is ineffective. 320 



The type of reactions directly catalyzed by the vitamin Bi 2 coenzyme 

 cannot be stated with certainty, but they definitely are involved in many 

 of the processes which utilize single carbon units. The vitamin appears 

 to be intimately associated functionally with folic acid and p-amino- 

 benzoic acid. 



To date, vitamin B12 has been implicated in the following processes: 



(1) the syntheses of purines and pyrimidines and their derivatives, 



(2) the syntheses of methionine and serine, and 



(3) the utilization of p-aminobenzoic acid and folic acid. 



The announcement of the isolation of thymidine 321 from antipernicious 

 anemia preparations resulted in a number of studies designed to determine 

 what relationship may exist between vitamin B12 and nucleic acid deriva- 

 tives. When tested on the bacteria which had been found to respond to 

 vitamin B i2 {Lactobacillus lactis Dorner and Lactobacillus leishmanii) , 

 it was found that either thymidine or the desoxyribosides of other pyrim- 

 idines and purines could be substituted for this vitamin. 322 - 323 > 324 « 325 

 Also it was shown that, in the presence of vitamin B 12 (and folic acid), 

 purines could be omitted from the medium used to culture L. Lactis. Z2& 



In considering possible relationship of vitamin B i2 to folic acid, it is 

 important to note that in the cases just mentioned vitamin B 12 and 

 folic acid cannot be effectively substituted for each other. An interesting 

 demonstration of their independence of function is contained in a report 

 in which it is implied that the vitamin B i2 required by L. leishmanii 

 can be replaced by thymidine but not by thymine, whereas folic acid can 

 be replaced (somewhat inadequately) by either thymine or thymidine. 326 

 On the basis of the nutritional needs of these two bacteria there has been 

 some speculation as to the possibility of vitamin B i2 functioning in the 



