BIOGENESIS OF THE B VITAMINS 



85 



cattle. 27, 39 Milk is reported to contain twice as much pantothenic acid 

 as the total dietary intake of the cow, but the assays on which such 

 reports are based are not entirely reliable due to incomplete extraction 

 (p. 34). Synthesis also takes place in rats, particularly in the cecum. 

 It has been estimated on the basis of balance studies that 10 to 60 per 

 cent of the requirement of the rat may be furnished in this way. 35 The 

 amount produced is dependent upon the type of diet and the intestinal 

 flora which is favored. Certain strains of C. diphtheriae, like yeasts, are 

 able to produce pantothenic acid when ^-alanine alone is supplied, indi- 

 cating that they possess the metabolic machinery for synthesizing pantoic 

 acid but not for producing /3-alanine. 40 Acetobacter suboxidans, on the 

 other hand, is stimulated by the pantoic acid portion of the pantothenic 

 acid molecule and evidently possesses the ability to synthesize /^-alanine 

 but not pantoic acid. 41 Present evidence seems to indicate that the bio- 

 synthesis of pantothenic acid occurs through the direct coupling of 

 ^-alanine and pantoic acid. A considerable amount of evidence (p. 465) 

 indicates that the /^-alanine is formed by the decarboxylation of aspartic 

 acid, while the pantoic acid has been suggested as arising from an amino 

 acid, pantonine (p. 289), thus: 



COOH 



CH 2 



CH— NH 2 



COOH 

 Aspartic Acid 



CH 2 OH 



CH 8 — C— CH, 



HC— NH 2 



COOH 

 "Pantonine" 



-co 2 



CH S 



k NH 2 — CH 2 — CH 2 — COOH 

 ^-alanine 

 CH 3 



CH 2 — C CH— COOH 



OH CH, OH 



Pantoic acid 



CH 2 OH 

 -C— CH, 

 CHOH 



<u 



" NH 

 CH 2 

 CH 2 

 COOH 



Pantothenic 

 acid 



Further discussion bearing on the mechanism of the biosynthesis of pan- 

 tothenic acid will be given in a later section (p. 464). 



The production of pantothenic acid by common strains of bakers' yeast, 

 in the absence of ^-alanine, is certainly not important, but other yeasts 

 and fungi which are able to grow on simple media undoubtedly produce 

 the whole molecule. No worthwhile information regarding the importance 

 of fungi as producers of pantothenic acid in the soil or elsewhere appears 

 to be available. 



