94 III. OXIDATION AND METABOLISM 



-H2O 

 CeHsCHOHCHaCOOH > CeHsCHrCHCOOH 



/3-Phenyl-/S-hydroxypropionic acid Cinnamic acid 



The Desaturation of /3-Phenyl-)3-Hydroxypropionic Acid by Removal of One Molecule 



of Water^!* 



Although similar dehydrogenations have not been reported in the non- 

 phenylated hydroxy fatty acids, the reaction is believed to occur in these 

 latter acids as well. The formation of a-imino acids from the correspond- 

 ing a-amino acids is a common example of Q;,/3-dehydrogenation hi another 

 group of compounds. 



(d') In the Metabolism of a,/3-Dideutero-Acids. — The data of More- 

 house'"" also support the hypothesis that Q;,/S-desaturation occurs. Thus, 

 when a:,|(3-dideutero]iutyric acid was fed to rats, the ^S-hydroxybutyrate ex- 

 creted contained only 4% of the orighial deuterium. However, when More- 

 house'"" fed ^,7-dideuterobutyrate, she was able to obtain five times the 

 amount of deuterium from the /3-hydroxybutyrate in the urine that was 

 present when the a,/3-acid was fed. Although this experiment may be inter- 

 preted as indication of a preliminary a,/3-dehydrogenation, Breusch' sug- 

 gests that /3-ketobutyric acid might be the first product formed. The enol 

 of this form might readily exchange its deuterium in the a-position with 

 protons of ordinary water.' Deuterium-free (S-hydroxybutyric acid would 

 be formed as the second step, as indicated below: 



CH3CHDCHDCOOH > CH3CHOHCH2COOH 



Qr,/3-Dideuterobutyric /3-Hydroxybutyric 



acid acid 



The reaction with /3,7-dideuterobutyric acid is pictured as follows:' 



CH2DCHDCH2-COOH > CH2D • CHOH • CH2 • COOH 



/3--v-Dideuterobutyric 7-Deutero-/3-hydroxybutyric 



acid acid 



Although the data of Morehouse'"" are not a definite proof of a,/3-dehydro- 

 genation, they do demonstrate that the 7-position is attacked very much 

 less readily than is the a- or /3-position ; this is in line with the /3-oxidation 

 theory. 



c' . The Behavior of a,/?-Unsaturated Acids: Crotonic acid, CHs-CH:- 

 CH-COOH, the simplest even-carbon member of the Q;,/3-unsaturated acids, 

 is metabolized in a manner similar to that of the corresponding saturated 

 acid, namely butyric acid. Thus, Blunden'"' reported that the quantity of 



'oo M. G. Morehouse, J. Biol. Chem., 129, 769-779 (1939). 



'°i H. D. Blunden, The Intermediary Metabolism of Butyric Acid as Determined from the 

 Physiological Behavior of the Various Four-Carbon Acids, Dissertation, Univ. Southern 

 California, 1938. 



I 



