194 PHYSIOLOGY OF THE FUNGI 



biotin-deficient microorganisms and found that it replaced biotin for 

 some fungi, while it acted as an antibiotin for some few others. Desthio- 

 biotin replaced biotin quantitatively for Ceratostomella ips. Goldberg 

 et al. (1947) found some homologues of biotin to inhibit growth of yeast 

 139 and Lactobacillus casei. Whether any of these biotin homologues 

 will replace biotin for other microorganisms must await further testing. 

 These preliminary results indicate that the length of the acidic side chain 

 of the biotin molecule is of great importance in biological activity. 



Oxybiotin is also known as 0-heterobiotin and has the same structure 

 as biotin except that the sulfur in the tetrahydrothiophene ring has been 

 replaced by oxygen. Pilgrim et al. (1945) found oxybiotin to be active 

 for Lactobacillus casei, L. arabinosus, and a strain of Saccharomyces cere- 

 visiae. Oxybiotin is apparently used as such and is not converted into 

 biotin by the organism (Axelrod et al., 1947). This is the only instance 

 that has come to our attention where a vitamer is used directly instead 

 of being converted into the vitamin. Rubin et al. (1945) had previously 

 reported that oxybiotin was converted into biotin. The cause of this 

 disagreement is unknown. 



Pimelic acid is a growth factor for certain strains of the diphtheria 

 bacterium (Mueller, 1937). It is reported (Du Vigneaud et al., 1942) 

 that pimelic acid replaced biotin and was probably the precursor in the 

 synthesis of biotin by a strain of the diphtheria organism. The higher 

 and lower homologs of pimelic acid were ineffective. The formula for 

 pimelic acid is HOOC— CH2— CH2— CHa— CH2— CH2— COOH. At 

 present there is no evidence that pimelic acid replaces biotin for the 

 fungi. This observation is supported by the findings of Robbins and Ma 

 (1942), who studied 13 biotin-deficient fungi. A favorable effect of the 

 presence of pimelic acid was reported by Eakin and Eakin (1942), who 

 found that Aspergillus niger synthesizes much more biotin in the presence 

 of pimelic acid than in its absence. Cysteine and also cystine increase 

 the synthesis of biotin. The lower homologues of pimelic acid (adipic, 

 glutaric, and succinic) were without effect, while the higher homologs 

 (suberic and azelaic) were as effective as pimelic acid. This is interesting, 

 inasmuch as homobiotin and bishomobiotin are reported inactive for 

 yeast growth (Goldberg et al., 1947). 



Mode of action. It has been assumed that biotin acts as a coenzyme 

 for various enzyme systems, but definite proof seems to be lacking, 

 Winzler et al. (1944) found that, when biotin was added to a biotin- 

 starved yeast, some time elapsed before any effect was noted. The order 

 of response was fermentation, respiration, and growth. The assimilation 

 of ammonia did not take place unless biotin was added. 



The presence of aspartic acid in the culture medium has been shown 

 to reduce the amount of biotin required by Torula cremoris (Koser et al., 



