THE PROTEINS AND THEIR METABOLISM 



109 



The fate of valin in the body is not definite. Dakin (1913) has found 

 that it does not give rise to either glucose or acetone bodies. From a priori 

 reasoning, and from experiences that were obtained with substances chem- 

 ically related to it, one would have expected the transformation into glu- 

 cose of three of its carbons. 



The fate of leucin is definitely known. It does not give rise to any 

 glucose, but gives rise to large amounts of |3-hydroxybutyric acid and 

 acetone. Baer and Blum, 1906 (a) ; Halsey, 1903; Dakin, 1913; Ringer, 

 Frankel and Jonas, 1913 (a) ; Embden Salomon and Schmidt, 1906). The 

 a-carbon is probably the first to suffer oxidation and the molecule becomes 

 converted into iosovalerianic acid, which on demethylation is converted 

 into butyric acid, and which on (3-oxidation is converted into P-hydroxy- 

 butyric acid, aceto-acetic acid and acetone. 



CH 3 CH 3 



\y 



CH 2 



P-CH 2 Deami- (3-CH 2 Oxida- 

 nation tion 



CH 3 CH 3 



v 



CII 



CH 3 CH 3 



\y 



P-CH 2 



2 Oxida- a-CH 2 Demethyl- 

 tion ation 



o-CHNH 2 



COOH 

 . Leucin 



O.CHOH 

 COOH 



a-CO 

 COOH 



COOH 



C0 2 



Isovalerianic 

 acid 



CH, 



CH, 



OH, 



CH 



CH 2 Oxidation CHOII Oxidation CO Decarboxylation CO 



CH 2 



COOH 



Butyric acid 



CH, 



COOH 



(3-hydroxy 

 butyric acid 



CH, 



COOH 



Aceto-acetic 

 acid 



CH, 



CO, 



Isoleucin and normal leucin. In Dakin's experiments (1913) we find 

 an increase of 3.8 and 2.9 grams of glucose after administering 15 

 grams of isoleucin. Dakin is not inclined to consider that as conclusive 

 proof that it is glucogenetic. From the structure of the normal leucin, 

 however, one may assume the possibility of sugar formation. Normal 

 valerianic acid may be formed after deamination and decarboxylation and 

 this has been shown to be glucogenetic to the extent of three of its carbons. 



