BIOTIN 333 



6. BIOTIN 



Biotin (vitamin H, coenzyme R) is required by many yeasts and 

 fungi; all the major taxonomic groups of the fungi are represented by 

 biotin-requiring types (5, 35, 67, 128, 161, 214, 219, 240, 241). The 

 absolute requirement is usually less than 5 t xg per liter (Figure 2). 



The role of biotin is not certain; in bacteria, it or a derivative of it 

 is probably involved in several enzymatic systems (126). Evidence from 

 studies of several fungi (111, 155, 190) implicates biotin in the synthe- 

 sis of aspartic acid, inasmuch as aspartate partially replaces biotin in 

 nutrition. It seems likely that the reaction affected by biotin is either 

 the carboxylation of pyruvic acid to yield oxalacetic acid or the conver- 

 sion of oxalacetate to aspartate (92): 



Pyruvic acid + C0 2 — » oxalacetic acid — > aspartic acid (2) 



A second probable function of biotin in fungi is in the synthesis of 

 essential fatty acids; oleic acid partially replaces biotin for a Neuro- 

 spora crassa mutant (111) and for OpJiiostoma pini (163). It must be 

 said that evidence for the essentiality of fatty acids for fungi is incom- 

 plete; the possibility is raised by (a) the stimulating effect of oleic acid 

 on growth (12, 84, 332) and (b) the occurrence in Neurospora crassa 

 of mutants requiring fatty acids (129). 



Less well-defined and probably indirect effects of biotin on fungi 

 include inhibition of growth of a pantothenicless mutant (228), inhibi- 

 tion of enzyme synthesis in one strain of Neurospora crassa (11), and 

 change in the growth pattern of the dimorphic Sporotrichum schencki 

 (160). Mitrula paludosa requires biotin only if ammonium nitrogen is 

 used in the medium (67). 



In relation to biosynthesis, the structures of three compounds are of 

 interest: 



O O 



II II 



/°\ /°\ 



HN NH HN NH 



II II 

 HC CH HC CH 



II II 



CH 3 GH 2 — (CH 2 ) 4 — COOH H 2 G CH 2 — (CH 2 ) 4 — COOH 



V 



Desthiobiotin Biotin 



