552 THE BIOCHEMISTRY OF B VITAMINS 



nutrition of the Allen strain of the organism. 57 Pimelic acid, however, 

 does not replace biotin or desthiobiotin for a majority of organisms requir- 

 ing biotin. 54 ' 58 Pimelic acid, and also suberic and azelaic acids, enhanced 

 effectively the biosynthesis of biotin in Aspergillus niger, an organism 

 which requires neither biotin nor pimelic acid. 59 The biosynthesis is fur- 

 ther enhanced by certain sulfur compounds, such as cystine and cysteine. 

 An increase in the accumulation of a substance similar to desthiobiotin in 

 the biotinless mutant of Penicillium chrysogenum, strain 62078, is ob- 

 tained on supplementing the medium with pimelic acid. 54 Hence, the 

 effects of pimelic acid and desthiobiotin appear to be those of precursors 

 of biotin as indicated below: 



HOOC— (CH 2 ) 6 — COOH — ^ 



CO CO 



/ \ / \ 



HN NH HN NH 



HC CH — > HC CH 



CH 3 CH 2 — (CH 2 ) 4 — COOH H 2 C CH— (CH 2 ) 4 — COOH 



\ / 



S 



Other Stimulatory Biotin Analogues. As indicated above, the oxygen 

 analogue of biotin and precursors of biotin replace the vitamin in the 

 nutrition of a wide variety of organisms. A considerable number of 

 analogues and derivatives of biotin and oxybiotin possess considerable 

 activity. The activities of these compounds are indicated in Table 13. 

 In many instances, biotin is formed from the derivatives, but in several 

 cases the activities appear to be inherent in the analogue. 



It is interesting to note that the methyl ester of biotin is inactive for 

 Lactobacillus casei but fully active for Saccharomyces cerevisiae. The 

 methyl ester of oxybiotin is slightly less active than the free acid for the 

 latter organism. 



The sulfoxide of biotin is as active as biotin for Saccharomyces cere- 

 visiae, but the sulfone which is an antagonist of biotin for Lactobacillus 

 casei has only slight growth-promoting activity for the yeast. This slight 

 activity is dependent upon the presence of aspartic acid in the medium. 

 Hence, it appears that the sulfone cannot replace all the functions of 

 biotin for this organism. Growth obtained with the sulfone at any con- 

 centration never attained more than 35 to 50 per cent of the maximum 

 growth obtained with cultures grown on biotin. The results indicate that 

 the sulfone may be utilized as such without prior conversion to biotin. 



The diamino acids obtained on hydrolysis of biotin, desthiobiotin and 



