344 VITAMIN REQUIREMENTS 



biosyntheses of riboflavin and of cobalamins are related (62, 266). 

 Streptomyces olivaceus incorporates labeled 5,6-dimethylbenzimidazole 

 without dilution into the cobalamin molecule (299); more recent and 

 still preliminary evidence is in favor of ^-aminolevulinic acid as a 

 precursor (250). 



15. VITAMINS K 



Vitamins K x and K 2 are required by higher animals. Both are de- 

 rivatives of 2-methyl-l,4-napthoquinone, and it appears that any con- 

 pound containing this nucleus is active in animals (3). 



Many bacteria produce vitamin K 2 (2), and the phthiocol of Myco- 

 bacterium tuberculosis — chemically 2-methyl-3-hydroxy-l,4-naphtho- 

 quinone — has K activity (3). The six fungi that have been tested (2) 

 do not have detectable vitamin K activity. Other 1,4-naphthoquinones 

 are known to be produced by fungi (Chapter 6), but none of these is 

 a 2-methyl derivative. 



No requirement for the K vitamins is known in the fungi; Almquist 

 (3) reviews the conflicting evidence for a K requirement in Mycobac- 

 terium paratuberculosis (313). 



Some compounds structurally related to vitamin K, specifically 2- 

 chloro-l,4-naphthoquinone (246) and 2,3-dichloro-l,4-benzoquinone, 

 are fungitoxic (Chapter 14). Menadione (2-methyl- 1,4-naphthoqui- 

 none) competitively inhibits the action of both of these compounds in 

 certain biological systems (246, 309). However, the fungitoxicity and 

 the reversal by menadione are not adequate evidence for a role of the 

 K vitamins in fungal metabolism; one may equally well consider the 

 antagonists as foreign toxicants competing for the same site of action 

 (309). 



16. OTHER GROWTH FACTORS 



The only well-characterized growth factor for fungi that has not so 

 far been mentioned is coprogen, required by species of Pilobolus and 

 first isolated from manure (107). Bioassays indicate that this factor 

 is manufactured by some other fungi and several actinomycetes (108), 

 and crystalline coprogen has been isolated from Penicillium sp. (193). 



Coprogen is related chemically and biologically to two other ma- 

 terials, ferrichrome and the Arthrobacter terregens factor. Ferri- 

 chrome and ferrichrome A are nitrogenous iron-containing pigments 

 of Ustilago sphaerogena (76, 176); the effect of zinc on synthesis sug- 

 gests that ferrichrome is a precursor of cytochrome c (177). The 



