342 VITAMIN REQUIREMENTS 



pantothenate (61, 315), and it has been reported that Polyporus texa- 

 )ius requires pantothenate (332). Pantothenicless mutants have been 

 obtained frequently in the fungi (83, 121, 195, 278). 



Pantothenic acid functions in metabolism as a constituent of the 

 larger molecule coenzyme A, an essential cof actor in a number of acyl 

 transfer and related reactions (147, 184). The effect of pantothenate 

 on carotenogenesis in Mucor hiemalis presumably results from an in- 

 crease in the rate of acetyl transfer (90). 



Presumably all fungi except those needing exogenous pantothenate 

 synthesize the vitamin; this is borne out by analysis of, for example, 

 Boletus edulis (40), Neurospora crassa (297), and a few other fungi 

 (181). The ultimate step in pantothenate synthesis is known to be the 

 coupling of pantoic acid and /^-alanine. This coupling is carried out 

 by growing cells, resting cells, and a cell-free preparation (acetone 

 powder) of Neurospora crassa (296). Surprisingly, the enzyme is found 

 also in a pantothenicless mutant, the cells of which do not under the 

 usual conditions of still culture form pantothenate from the two pre- 

 cursors (295). However, it has been found that the coupling reaction 

 above does proceed in "pantothenicless" cells grown under aeration 

 (297). Either we have here in still culture a gene-controlled suppres- 

 sion of an enzyme, or the mutant strain is unable under limited aera- 

 tion to provide the energy necessary for the formation of the peptide 

 bond of pantothenic acid. 



The origin of the pantoic acid moiety in fungi is not known; in bac- 

 teria, p-aminobenzoic acid is involved, and there is some evidence that 

 a-ketoisovaleric acid is a precursor of pantoic acid (266). 



13. PTEROYLGLUTAMIC ACID 



Pteroylglutamic acid (vitamin Be, Lactobacillus casei factor, folic 

 acid, folacin) and its relatives are required by microorganisms and 

 higher animals; probably the several active compounds are all con- 

 verted to the same form (265). Venturia inaequalis is reported to be 

 stimulated in its growth by pteroylglutamic acid (63); no fungi or 

 actinomycetes are known to require the factor. 



A substance active for Lactobacillus casei is produced by several 

 fungi, including species of Absidia, Aspergillus, Ghaetomium, Circi- 

 nella, Fusarium, Monascus, Mucor, Neurospora, Pencillium, and Rhi- 

 zopus (30, 164, 178). The identity of this product is uncertain. Citro- 

 vorum factor, another member of this group of compounds, is formed 

 by Streptomyces griseus (59). 



Rhizopterin, N-formylpteroic acid, is formed by Rhizopus nigricans 



