BIOGENESIS OF THE B VITAMINS 89 



Few studies have dealt with bacterial growth in relation to inositol 

 synthesis. In the previously mentioned study of Thompson, 5 its produc- 

 tion by five diverse bacteria was demonstrated. One study indicated that 

 it is not produced to a substantial degree by intestinal organisms in 

 rats. 34 The relative abundance of inositol in plant materials 56 > 57 sug- 

 gests that it is probably synthesized by plants. It is stimulatory to certain 

 fungi, but in view of the ability of many of these organisms to grow on 

 simple media, it is presumably synthesized by them. 



Choline is probably widely synthesized in nature. Few bacteria have 

 been found to require it, 58 and wild strains of Neurospora evidently 

 synthesize it. 59 In animals, as in Type III Pneumococci, 58 methionine and 

 other compounds containing available methyl groups serve as precursors. 

 Ethanolamine is probably important as a precursor in the biosynthesis 

 of choline (p. 353). Choline biosynthesis has been extensively studied 

 and it is now felt that the exact sequence involved is well known. In brief, 

 it may be indicated thus: 



CH 2 OH 



-CO2 

 CH 2 NH 2 



COOH 



Serine 



CH 2 OH 



-> CH 2 



NH 2 



Ethanolamine 



CH 2 OH 



+CH 3 I 



► CH 2 



NH— CH 3 



CH 2 OH 

 CH 2 



■> N— CH 3 



CH 3 



+CH 3 



CH 2 OH 



CH 3 



+N 



CH 3 CH 3 

 Choline ion 



Certain aspects of this sequence of reactions are considered in greater 

 detail in a later section (p. 353). 



p-Aminobenzoic acid, like choline, is probably produced widely in 

 nature. Although a considerable number of bacteria are stimulated by 

 its presence in the culture medium, Peterson and Peterson 1 list 13 

 bacteria which have been found to synthesize it. Wild strains of Neuro- 

 spora synthesize this substance as do yeasts. Presumably green plants 

 do as it enters into the make-up of folic acid, but no direct evidence on 

 this point has been found. 



