BRANCHED-CHAIN ACIDS 299 



CH3-(CH2)2-CH(C3H7)-CHi-CH2COOH > Excreted unchanged 



7-Propylheptanoic acid 



CH3(CH2)3CH(C3H7)CH2CH2COOH > CH3-(CH2)3-CH(C3H7)COOH 



7-Propyloctanoic acid a-Propylhexanoic acid 



CH3(CH2)2CH(C3H7)-(CH2)3-COOH > CH3(CH2)2-CH(C3H7)-CH2-COOH 



5-Propyloctanoic acid ^-Propylhexanoic acid 



CH3-(CH2)2CH(C3H7)-(CH2)4COOH > CH3(CH2)2-CH(C3H7)(CH2)2-COOH 



5-Propylnonanoic acid 7-Propylheptanoic acid 



CH3-(CH2)2CH(C3H7)(CH2)5-COOH > CH,-(CH2)2-CH(C3H7)CH2-COOH 



f-Propyldecanoic acid /3-PropyIhexanoic acid 



CH3-(CH2)7-CH(CH3)(CH2)2COOH > HOOC-(CH2)7-CH(CH3)-COOH 



7-Methyldodecanoic acid a-Methylsebacic acid 



Although the reaction products were formed in all cases, the quantities iso- 

 lated were in most cases quite small. 



WeitzeP^ observed that various a-substituted alkyl myristates and 

 stearates were readily absorbed by dogs. The methyl-substituted acids 

 were completely metabolized; however, when an ethyl side chain was 

 present, and especially when the substituent consisted of a propyl or butyl 

 group, the corresponding adipic acids were excreted in the urine. This 

 indicates that no steric hindrance occurs in the oxidation of the acids 

 having the methyl group in the side chain. However, when the lateral 

 chains are longer, a notable part of the fatty acid undergoes co-oxidation. 

 This is the first evidence of co-oxidation of fatty acids longer than C12. 



Annison and Pennington-* demonstrated that the branched-chain acids 

 can be utihzed by isolated tissues. Thus, isobutyric acid ((CH3)2:CH-- 

 COOH), isovaleric acid ((CHv),:CH-CH2-C00H) and racemic a-methyl- 

 butyric acid (CH3CH2CH(CH3) -COOH), as well as n-valeric acid (CHs-- 

 (CHojs-COOH), were shown to be metabolized by sheep rumen epithelium, 

 as well as by liver and kidney slices. Both n- and isovaleric acid caused an 

 increase in ketone body production over the controls. The metabolism 

 of iso\'aleric acid by rumen and liver tissue was augmented in the presence 

 of CO2. This is in harmony with the report of Coon^^ to the effect that a 

 C02-fixation occurs during the intermediary metabolism of the latter acid. 

 As would be expected, it was demonstrated that appreciable quantities 

 of acetic and propionic acids were produced during the metabolism of n- 

 valeric acid. 2"* El-Shazly^® also identified 2-methylbutyrate, isovalerate, 



» G. Weitzel, Z. physiol. Chem., 287, 254-296 (1951). 



" E. F. Annison and R. J. Pennington, Biochem. J., 52, ix (1952). 



26 M. J. Coon, J. Biol. Chem., 187, 71-82 (1950). 



2« K, El-Shazly, Biochem. J., 51, 640-647, 647-653 (1952). 



