738 METABOLISM 



first oxidation product formed from it in the body seems to be (3-oxybuty- 

 ric acid, CH 3 CHOHCH 2 COOH. This then becomes oxidized to form a 

 body having the formula CH 3 COCH 2 COOH, acetoacetic acid, which, on 

 further oxidation, readily yields CH 3 COCH 3 , or acetone. These sub- 

 stances (/?-oxybutyric acid, acetoacetic acid and acetone) appear in the 

 urine during carbohydrate starvation, as in diabetes. 



It might be objected, however, that a chemical process occurring under 

 abnormal conditions need not also occur in the normal animal. That it 

 probably does, however, is indicated by the results of the experiments 

 of Knoop and of Embden and his coworkers. Knoop conceived the idea 

 of introducing into the fatty-acid molecule some group which is resistant 

 to oxidation in the body. The phenyl group (C 6 H 5 ) was found to have 

 this effect. By feeding an animal with the phenyl derivatives of acetic, 

 propionic, butyric, and valeric acids, it was found that the urine con- 

 tained either hippuric (see page 663) or phenaceturic acid. Both of 

 these are compounds of aromatic acids with glycocoll or aminoacetic 

 acid (CH 2 NH 2 COOH), one of the protein building-stones and always 

 available in the organism to form such compounds, thus : 



( 1 ) C C H 5 COOH + CH 2 NH 2 COOH = C 6 H 5 CONHCH 2 COOH. 



(benzole (glycocoll) (hippuric acid) 



acid) 



( 2 ) C 6 H 5 CH 2 COOH + CH 2 NH 2 COOH C C H 5 CH 2 CONHCH 2 COOH. 

 (phenylacetic (glycocoll) (phenaceturic acid) 



acid) 



When either benzoic acid (C 6 H 5 COOH) or phenylacetic acid (C 6 H 5 CH 2 - 

 COOH) is formed in the body as a result of the oxidation of phenyl 

 derivatives of the higher fatty acids, the acid combines with glycocoll 

 according to the above equations. From this it follows that if oxidation 

 occurs so that two C-atoms are thrown off at a time (/3-oxidation), fatty 

 acids with an even C-atom chain should yield hippuric acid, and those 

 with an uneven chain, phenaceturic. This was found to be the case, as 

 the accompanying table shows. 



acid 



Phenylpropionic acid, C 6 H 5 . CH 2 . CH 2 . COOH C 6 H 5 .COOH Hippuric acid 



Phenylbuty ric acid, C 6 H B . CH 2 . CH 2 . CH 2 . COOH C H 5 . CH 2 . COOH Phenaceturic 



acid 

 Phenylvaleric acid, C 6 H 5 . CH 2 . CH 2 . CH . CH 2 . COOH C H 5 . COOH Hippuric acid 



(From Dakin.) 



