556 THE BIOCHEMISTRY OF B VITAMINS 



Nevertheless, a few of these analogues appear to be very potent in 

 preventing the utilization of desthiobiotin for certain organisms (Table 

 14). This is especially true of DL-2-oxo-4-imidazolidinecaproic acid for 

 Escherichia coli. Since biotin prevents the inhibition noncompetitively, 

 the analogue appears to prevent the conversion of desthiobiotin to biotin 

 (p. 468). Whether a similar situation exists with other analogues has 

 not been determined. In some cases both the conversion of desthiobiotin 

 to biotin and the utilization of biotin may be prevented by the inhibitor. 



Table 15. Sulfide and Sidfone Analogues of Biotin. 



Molar Inhibition Ratio 



" Also inhibitory to Lactobacillus arabinosus :ui<l Staphylococcus aureus.™ 

 b A mutant strain requiring biotin or desthiobiotin for growth. 



Desthiobiotin is reported to inhibit the functioning of biotin in Sordari 

 fimicola and Ceratostomella pini 416. Desthiobiotin is also reported to 

 have an inhibitory effect on the growth of tumors. 70 The response of 

 Lactobacillus arabinosus to biotin is increased by the presence of desthio- 

 biotin, even though the desthio compound is inactive alone. 51 



Neither 5-methyl-2-oxo-4-imidazolidinebutyric acid 64 nor 5-methyl-4- 

 hexyl-2-imidazolidone 66 has appreciable inhibitory activity for either 

 Lactobacillus casei or Saccharomyces cerevisiae. 



Sulfide and Sulfone Analogues of Biotin. The most potent inhibitors 

 of the utilization of biotin which have been reported are the homologues 

 of biotin, and the sulfone of biotin and its homologues. 48, 54, n Of these, 

 biotin sulfone and DL-homobiotin are the most effective antagonists of 

 biotin, as indicated in Table 15. When comparing the potencies of vitamin 



