CHAPTER VII 



THE METABOLISM OF BRANCHED-CHAIN 



ACIDS, HYDROXY AND KETO ACIDS, 



DICARBOXYLIC ACIDS, TRICARBOXYLIC 



ACIDS, FATTY ACID AMIDES, FATTY 



ACID ALDEHYDES, AND HYDROCARBONS 



When the nature of a fatty acid is altered by the presence of a side chain, 

 of an hydroxy! or of a ketone group, its metabolism may be markedly al- 

 tered from that of the normal straight-chain acid. The presence of more 

 than one carboxyl group poses a new problem in oxidation, and unique 

 properties and a separate metabolism may be expected of the polycar- 

 boxylic acids. Likewise, the behavior of the fatty acid residue is altered 

 when the carboxyl group is replaced by the amide group, as in the fatt}' 

 acid amides, or by the aldehyde group (fatty aldehydes). Finally, a still 

 greater alteration in metabolism is to be expected in the hydrocarbons than 

 in any of the fatty acid derivatives listed above. 



1. Branched-Chain Acids 



The metabolism of branched-chain acids has been extensively investi- 

 gated in animals and in man. The most important factor which influences 

 the course of the metabolism is the position of the side chain in relation 

 to the carboxyl group. The nature of the substituent group likewise pro- 

 vides a situation which results in a variation in metabolism. The altera- 

 tion in the metabolism of the branched-ehain acids from that of the straight- 

 chain compounds will likewise be related to the extent to which the usual 

 enzyme systems may be displaced and prevented from combining mth the 

 substrate by the altered configuration of the molecule. 



In contradistmction to the disturbing influence of the side chain on the 

 metabolism of the fatty acid in the animal, such variations in structure 

 have little influence on the utilization of the fatty acids by bacteria, Ac- 



291 



