METABOLISM OF THE B VITAMINS 363 



no pantoyl lactone in the urine, and that the lactone administered intra- 

 venously or orally is recovered in the urine quantitatively and unchanged ; 

 hence hydrolysis of the vitamin molecule probably does not normally 

 occur to any appreciable extent. 178 Since the tissue vitamin is almost 

 solely in the form of the coenzyme, it would seem that the search for 

 traces of coenzyme fragments in the urine may well lead to clues as to 

 the exact structure of this coenzyme. Synthetic pantothenyl alcohol is 

 converted by the body to pantothenic acid, 179 but since this former com- 

 pound apparently does not appear in nature, the reaction has no great 

 significance. 



H 



T 

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Lumichrome 



Little is known of the breakdown of folic acid in the body, but it is 

 known that "conjugase" of the liver, kidney and pancreas converts the 

 triglutamate and heptaglutamate to folic acid. 180 Strangely enough, in 

 vitro studies with chicken pancreas conjugase have shown that only the 

 terminal glutamic acid molecule is removed from the triglutamate, so 

 that there is a considerable lack of understanding of how folic acid is 

 ultimately produced in vivo. 181 Even in sprue, administered pteroyl 

 triglutamate is converted to the monoglutamate, as indicated by urinary 

 excretion of the latter. 182 The fact that folic acid-free liver extracts 

 further increase the excretion of folic acid in this case suggests that the 

 metabolism of the conjugates is in some manner mediated by the ery- 

 throcyte maturation factor. 



Although little is known of the normal metabolism of p-aminobenzoic 

 acid, larger amounts when administered are excreted as the acetylated 

 product. 183 Normal rats acetylate about 70 per cent of the excreted por- 

 tion of a 1 to 2.5-mg dose of p-aminobenzoic acid, and this ability is 

 decreased in pantothenic acid-deficient rats. 184 Sulfanilamide is similarly 

 acetylated in the animal body, 185 and if, as seems likely, the mechanism 

 is the same, the process involves adenosine triphosphate, acetate, and 

 coenzyme A. 186 The activity of liver preparations in this regard suggests 

 that this organ is at least one major site of the reaction. Since however 

 all these considerations refer to levels of p-aminobenzoic acid that are 

 somewhat above the physiological range, there can be no absolute cer- 



