264 VI. ACETIC, FORMIC, AND PROPIONIC ACIDS 



The ability of the animal body to bring about an acetylation is dependent 

 upon the presence of an adequate supply of CoA. Thus, Shils et al?^ 

 reported that, in rats whose tissues had a subnormal CoA content as a 

 result of a diet deficient in pantothenic acid, the acetylation of sulfanilamide 

 was markedly depressed, although this function remained normal in thia- 

 mine deficiency. Riggs and Hegsted'^^ noted that the acetylation of -p- 

 aminobenzoic acid was dramatically reduced in rats suffering from panto- 

 thenic acid or riboflavin deficiency; some reduction was also observed when 

 the amount of thiamine was deficient. 



a. Acetylation of Amino Acids and Amides. Knoop'^^ originally believed 

 that acetylation was a normal process in the metabolism of amino acids. 

 He based this conclusion upon the following series of experiments: When 

 DL-phenylaminobutyric acid (CeHB-CHz-CHa-CHCNHs) -COOH) was fed 

 to dogs, the optically active acetyl compound, acetyl-D-phenylaminobutyric 

 acid (C6H5-CH2-CH2-CHNH(COCH3)-COOH), appeared in the urine." 

 After the corresponding keto compound (C6Hb-CH2-CH2-CO-COOH) 

 was fed, the same acetyl compound was recovered from the urine as had 

 been excreted after the ingestion of the racemic amino acid. On the other 

 hand, when acetyl-DL-phenylaminobutyric acid was administered to dogs, 

 an excess of acetyl-L-phenylaminobutyric acid appeared in the urine.^^ 

 This showed that the body was able to oxidize the acetyl-D compound 

 better than the acetyl-L-acid, and the conclusion was drawn that the 

 dextrorotatory amino acid was probably the one corresponding in spatial 

 configuration to the naturally occurring amino acid series. 



In a further consideration of these results, Knoop and Blanco''^ reasoned 

 that the DL-amino acid could not have been directly acetylated, or the 

 acetyl-L acid would have appeared in the urine, rather than the acetyl-D 

 compound which was actually found. Ivnoop was of the opinion that the 

 isolation of acetyl-D-phenylaminobutyric acid affords excellent support 

 for the hypothesis that the amino acid is first deaminated to the keto acid; 

 the acetyl-D-phenylaminobutyric acid then arises by asymmetric synthesis. 

 The results obtained with phenylaminoacetic acid (CeHe • CHNH2 • COOH) 

 were similar to those in the case of the higher homolog. 



However, in a continuation of their work, Knoop and Blanco^^ found that 

 the compound excreted in the urine after the feeding of acetyl-DL-phenyl- 

 alanine was the levorotatory acetylphenylalanine. These workers inter- 



■>* M. E. Shils, H. M. Seligman, and L. J. Goldwater, /. Nutrition, 37, 227-235 (1949). 



" T. R. Riggs and D. M. Hegsted, J. Biol. Chem., 178, 669-675 (1949). 



'6 F. Knoop, Z. physiol. Chem., 67, 489-502 (1910). 



" F. Knoop and E. Kertess, Z. physiol. Chem., 71, 252-265 (1911). 



7« F. Knoop and J. G. Blanco, Z. physiol. Chem., I46, 267-275 (1925). 



