96 III. OXIDATION AND METABOLISM 



unsaturated fatty acids may be oxidized to the ketone bodies in a manner 

 similar to that of the corresponding saturated acids. 



(6) Pjy-DehTjdrogenation. Kleinzeller""^ demonstrated that the pathway 

 of metaboHsm of the simplest /3,7-unsaturated acid, vinylacetic acid (CH2:- 

 CH-CH2-C00H) may be similar to that of butyric acid. Acetoacetate was 

 also shown to arise when vinylacetic acid was oxidized by the liver cyclo- 

 phorase system. ^"^'^"^ Presumably, this may mean that a shift of the 

 double bond from the /3,7- to the Q;,|8-position occurs as a preliminary to 

 oxidation. 



(c) 9,10-Dehydrogenation. There is considerable evidence that the 

 animal possesses the ability to bring about a dehydrogenation at the 

 9,10-position. Thus, the classical studies of Schoenheimer and Ritten- 

 ]3gj.g 106 g^j^(^ those of Stetten and Schoenheimer,'"^ although not defining the 

 site of dehydrogenation, were generally accepted as being concerned with 

 the formation of double bonds in the 9,10-positions. Lang and Adickes^**^ 

 report that oleic acid originates when a fatty acid dehydrase acts on stearic 

 acid, but that no Q;,|S-octadecenoic acid is formed. The dehydrogenase sys- 

 tem employed by Champougny and LeBreton^"^ likewise produces de- 

 saturation at the 9 : 10 position in the case of octadecanoic acid. 



a'. Fatty Acids Effective as Substrates. In practically all cases, mono- 

 ethenoid acids which occur physiologically have the double bond in the 

 9,10-position, irrespective of whether they contain only ten carbons or more. 

 This is also true for the poly-unsaturated acids, linoleic and Hnolenic, but 

 not for arachidonic acid, which is 5,8,11,14-eicosatetraenoic acid. 



The fatty acids occurring naturally include 9,10-decenoic acid, CH2:CH.- 

 (CH2)7.COOH, first detected in butterfat by Smedley"" and isolated by 

 Bosworth and Brown, "^ as well as a series of higher homologues demon- 

 strated in butterfat by Hilditch and Longenecker,^^^ including: 



9,10-dodecenoic acid (0.9%), CH3-CH2-CH:CH-(CH2)7COOH; 

 9,10-tetradecenoic acid (1.7%), CH3-(CH2)3-CH:CH-(CH2)7-COOH; 

 9,10-hexadecenoic or palmitoleic acid (3.7%), CH3-(CH2)5-CH:CH-(CH2),-COOH; 

 9,10-decenoic acid, CH2:CH(CH2)7COOH, 



was present to the extent of 0.4%. 



10s A. Kleinzeller, Biochem. J., 37, 678-682 (194.3). 



i»« R. Schoenheimer and D. Rittenberg, /. Biol. Chem., 113, 505-510 (19.36). 



10' De W. Stetten, Jr., and R. Schoenheimer, J. Biol Chem., 133, 329-345 (1940). 



108 K. Lang and F. Adickes, Z. physiol. Chem., 262, 123-127 (1939-1940). 



109 J. Champougny and E. LeBreton, Compt. rend. soc. bioL, I4I, 450-453 (1947) 

 "0 I. P. Smedley, Biochem. J., 6, 451-461 (1912). 



I'l A. W. Bosworth and J. B. Brown, J. Biol. Chem., 103, 115-134 (1933). 



"2 T. P. Hilditch and H. E. Longenecker, /. Biol. Chem., 122, 497-506 (1938). 



I 



