VITAMINS 



245 



wise many of the lower organisms such as yeasts, bacteria, and fungi 

 do require biotin for normal development. No biotin deficiency has been 

 observed in human beings consuming their customary diets. The daily 

 intake of biotin on an average diet ranges from 25 to 50 ixg., and the 

 urine and feces together may contain from two to five times these 

 quantities. 



Fig. 9-13. 



Courtesy of the S. 

 Biotin. 



M. A. Corporation. 



Biotin appears to function (possibly in the form of a coenzyme, al- 

 though none has yet been identified) as a catalyst for one of the reac- 

 tions of the citric acid cycle (p. 330) : 



COo + CH3— CO— COOH 

 Pyruvic acid 



-> HOOC— CHo— CO— COOH 

 Oxalacetic acid 



Further, certain lactobacilli which normally require biotin grow well with- 

 out it if oleic acid is supplied instead. This observation indicates some 

 kind of a metabolic relationship between these two substances, perhaps 

 participation of biotin in the biosynthesis of oleic acid. The vitamin is 

 also required for deamination by bacterial cells of serine, threonine, and 

 aspartic acid. 



Chemical nature 



Biotin has a two ring structure with a side chain attached to one of 

 the rings. It is an acid, as is indicated by the carboxyl group in the 

 side chain. Note the urea-like structure in one of the rings {A) and the 



