292 VII. ACIDS, AMIDES, ALDEHYDES AND HYDROCARBONS 



cording to Weitzel and Schraufstatter,^ the utilization of the fatty acids by- 

 bacteria is inhibited to a progressively greater degree as the chain length 

 increases, but this is not influenced by methyl-substitution in the side chain. 

 In the case of the molds, such as Penicillium glaucum (blue-green cheese 

 mold). Thaler et al.^ reported that the a-methyl group caused no poisoning 

 action on growth. Thus, the mold grew well in the presence of a-methyl- 

 butyric, cc-methylcaproic, or a-methyllauric acids, with the formation 

 of ketones. It was suggested that the course of metabolism involves the 

 following changes: saturated fatty acid, Q!,/3-unsaturated fatty acid, ^- 

 hydroxy-fatty acid, jS-keto-fatty acid, and methylketone. On the other 

 hand, ;S-methyl-/3-hydroxypelargonic acid and j8-methyl-;5-hydroxylauric 

 acid could not serve as sources of carbon in the culture medium for P. 

 glaucum; moreover, no methylketones resulted from mold action on these 

 derivatives. 



(/) a-Substituted Acids 



Kay and Raper^ early called attention to the aberrant behavior of sev- 

 eral a-phenyl-substituted acids. Thus, a-phenylpropionic acid (hydra- 

 tropic acid), CH3-CH(C6H5) -COOH, was oxidized to the extent of 70%, 

 while the unoxidized fraction was excreted as the glucuronate. a-Phenyl- 

 ;S-hydroxypropionic acid (inactive tropic acid), HOCH2 -011(06115) COOH, 

 was excreted unchanged to the extent of 90%. When the hydroxyl group 

 was also on the a-carbon, as in inactive atrolactic acid (OH3 -0(011)- 

 (ObHb) -OOOH), 80% of the resulting compound was excreted. Finally, 

 atropic acid, C6H5-0(:OH) -COOH, was completely oxidized when ad- 

 ministered in small doses. 



When a methyl group is substituted in the a-position, the acids are 

 readily oxidized in the body to yield the same end-products as the corre- 

 sponding unsubstituted acids. ^-^ Since the a-methyl-substituted acids have 

 two j9-carbon atoms, oxidation may involve either one. If it attacks the 

 methyl group, it will be removed, and oxidation of the resulting straight- 

 chain acid will be normal. If oxidation results on the second /3-group, 

 the cleavage of a three-carbon fragment will occur. 



Kay and Raper^ were of the opinion that the first pathway best explained 



1 G. Weitzel and E. Schraufstiitter, Z. physiol. Chem., 285, 172-182 (1950). 



2 H. Thaler, A. Schottmayer, I. Stahlin, and H. Beck, Biochem. Z., 320, 87-98 (1949). 



3 H. D. Kay and H. S. Raper, Biochem. J., 16, 465-474 (1922). 

 « H. D. Kay and H. S. Raper, Biochem. J., 18, 153-160 (1924). 



6 M. J. Coon and N. S. B. Abrahamsen, /. Biol. Chem., 195, 805-812 (1952). 



