BRANCHED-CHAIN ACIDS 297 



observed that, following the luhninisti-ntion of «-ethyl-substituted acids 

 such as a-ethylbutyric acid, Cll3Cli2-C'I[(C'jH5) COOH, and a-ethyl-n- 

 caproic acid, CH3 • CH2 • CH2 • CH2 • CH(C2H5) • COOH considerable amounts 

 of glucuronides were also excreted. These results are in harmony with 

 those of Carter,^ in which the failure of a-ethyl and a-propyl acids to be 

 metaboHzed was noted. Akiya and Yamakawa^^ reported that a number 

 of acids, including : 



2-methylcaprylic acid (CH,-(CH2)5CH(CH3)-COOH) 



3-methylnonanoic acid (CH3-(CH2)5-CH(CH3)-CH2-COOH) 



3-ethylcaproic acid (CH3(CH2)2-CH(C2H5)-CH2-COOH) 



dibutylacetic acid ((CH3(CH2)3)2:CH-COOH) 

 dipropylpropionic acid ((CH3 • CH2 • CH2)2 : CH • CH2 • COOH) 



were excreted unchanged by rabbits, and also as the dicarboxylic acids after 

 co-oxidation. 



In the comprehensive studies of Keil and co-workers, ^^~^^ it was found 

 that methyl-substituted fatty acids were largely metabolized. Thus, after 

 the feeding of 



a-methyl-dodecanoic acid (CH3-(CH2)9-CH(CH3)-COOH) 

 ;8-raethyl-dodecanoic acid (CH3-(CH2)8-CH(CH3)-CH2-COOH) 

 5-methyldodecanoic acid (CH3-(CH2)6- CH(CH3)-(CH2)3- COOH) 



to dogs in the form of triglycerides, without added fat, there was only a 

 slight increase in the m-mary acids excreted, as contrasted with the results 

 of the administration of unbranched dodecanoic acid or tridecanoic acid. 

 Weitzel and co-workers^^ demonstrated that one methyl group attached to 

 carbon-atom 2 (a) hindered oxidation more than did three methyl groups 

 on a long-chain fatty acid at positions 3, 7, and 11 to the carboxyl. How- 

 ever, when ethyl-substituted acids were fed to dogs in a 1:3 mixture in 

 cocoa fat, as triglycerides, amounts of ether-soluble metabolic end-products 

 up to 50% of the weight of the ingested acids were found to be excreted in 

 the urine. The follo\Ning end-products were obtained from the several 

 acids administered:'* 



'^S. Akiva and T. Yamakawa, ./. Phann. Soc. Japan, 70, 477-80 (1950); Chein. 

 Ahsl., 45, 3479 (1951). 



'« W. Keil, Z. physiol. Cheni., 274, 175-185 (1942). 



" H. Appel, H. Bohm, W. Keil, and G. Schiller, Z. physiol. Chem., 274, 186-205 

 (1942). 



'8 W. Keil, Z. physiol. Chem., 276, 26-32 (1942). 



" G. Weitzel, A. FretzdorfT, J. Wojahn, W. Savelsberg, and K. Thomas, Nature, 

 163, 406-407 (1949). 



