VITAMINS 251 



cyanide group (CN) bound in a coordination complex with the cobalt 

 atom, which can be replaced by CI, SO4, OH, SCN, or other groups to 

 produce analogs of the natural substance. The analog containing the 

 water molecule has been called vitamin Bi2a and is apparently identical 

 with another preparation provisionally designated Bi^b- Brink and co- 

 workers have suggested that the B12 molecule, except for the cyanide 

 group, be called cohalamin. By this nomenclature, vitamin B12 would 

 be named cyano-cobalamin and Bi2a, hydroxo-cobalamin. All of these 

 various forms of the vitamin have approximately the same kind and 

 amount of biological activity. 



Physiological function 



In the short period since its isolation vitamin B12 has acquired excep- 

 tional practical importance because of its demonstrated usefulness in 

 pernicious anemia and related diseases, in livestock feeding, and in human 

 nutrition. Its absence from the tissues of the body is apparently the 

 specific cause of pernicious anemia. Injection of as little as 1 fig. per 

 day dramatically alleviates the symptoms of this disease. It is less 

 effective when given by mouth because pernicious anemia patients lack 

 some substance ("intrinsic factor") in the gastric juice which protects 

 vitamin B12 and favors its absorption. Small doses of vitamin B12 are 

 also effective in sprue and other macrocytic anemias. See Plate IV op- 

 posite p. 223. 



It has been known for many years that animal protein supplements 

 {e.g., meat scraps, dried whey, etc.) used in livestock feeding contain some 

 factor necessary for growth of animals fed only plant proteins. This un- 

 known substance was called the animal protein factor (APF). Vitamin 

 B12 is certainly the chief and, perhaps, the only component of APF. 

 Because of its high APF potency, it is now widely used in animal feeds. 

 Availability of vitamin Bio has made possible the use of larger proportions 

 of the relatively cheap plant protein concentrates (soybean, linseed, 

 cottonseed meals) , which are more plentiful than those from animal 

 sources, and has thus been a boon to livestock production. 



The vitamin B12 used in feeds is obtained almost exclusively from 

 fermentation sources, and especially as a by-product of the fermentations 

 which produce such antibiotics as aureomycin, terramycin, and strepto- 

 mycin. It was noted that crude B12 concentrates from these sources gave 

 greater growth responses in some species than could be accounted for by 

 their B12 content. The extra effect was traced to the antibiotics still 

 present as impurities in the concentrates. This discovery has opened 

 new vistas in the science of nutrition, since by use of this combination 

 faster growth rates have been achieved than had previously been con- 

 sidered optimal on the best mixtures of natural foods. The effect is 



