SATURATED FATTY ACIDS 11 



suit of successive condensations of a number of acetaldehyde molecules by 

 a series of reactions similar to the aldol condensation. Although it is now 

 known from experiments with isotopically marked acetaldehyde that this 

 compound is not used directly for the synthesis of fatty acids/"- ^^ Brady 

 and Gurin^2 demonstrated that the acetaldehyde carbon can serve as a 

 source of fatty acid after first being converted to acetate. 



b. Ethanol as the Two-Carbon Fragment Required for Fatty Acid Syn- 

 thesis. Masoro and Abramovitch^^ reported that ethanol can be con- 

 verted to fatty acids by liver slices but not to any considerable extent by 

 kidney slices; however, the kidney surpasses the liver in the rate at which 

 it can utilize ethyl alcohol. It is not unexpected that the carbons of un- 

 oxidized ethanol might be converted to fatty acids, since it has been 

 recognized for a number of years that the reverse change, namely the 

 conversion of acetaldehyde to alcohol, can take place. Thus, Battelli 

 and Stern^^ demonstrated this reverse change as part of a Cannizzaro re- 

 action which is mediated by an enzyme, aldehyde mutase. Neuberg and 

 Windisch^^ described the acetic acid fermentation in which two molecules 

 of acetaldehyde react to give one molecule each of ethanol and acetic acid. 

 The ethanol is then reconverted to acetaldehyde. Since acetaldehyde can 

 be built into fatty acids, it is logical to suppose that it maj'- be an inter- 

 mediate in the conversion of ethanol to fatty acids. 



c. Acetate as the Two-Carbon Fragment Required for Fatty Acid Syn- 

 thesis. A number of investigations have pointed to acetate or to a closely 

 related substance as the active intermediate in fat synthesis. Thus, the 

 original observation of Embden and Oppenheimer, ^^ made in 1912, in which 

 it was shown that acetoacetic acid appeared in the blood after the surviving 

 liver of the dog was perfused with blood to which pyruvate had been added, 

 led to the discovery by Loeb^^ and by Friedmann^^ that acetate was prob- 

 ably an mtermediate, since it also gave rise to acetoacetate under similar 

 experimental conditions. Smedley-MacLean and Hoffert^^ were the first 



" J. W. Cornforth and G. Popjdk, Unpublished observations, 1952; cited by G. Popjdk 

 in R. T. Williams, Lipid Metabolism, Biochem. Soc. Symposia, No. 9, Cambridge Univ. 

 Press, 1952, p. 37. 



" G. L. Curran and D. Rittenberg, /. Biol. Chem., 190, 17-20 (1951). 



12 R. O. Brady and S. Gurin, /. Biol. Chem., 189, 371-377 (1951). 



12 E. J. Masoro and H. Abramovitch, Federation Proc, 12, 94 (1953). 



1* F. Battelli and L. Stern, Compt. rend. soc. biol, 68, 742-744 (1910). 



'6 C. Neuberg and F. Windisch, Biochem. Z., 166, 454-481 (1925). 



i»G. Embden and M. Oppenheimer, Biochem. Z., 45, 186-206 (1912). 



"A. Loeb, Biochetn. Z., 47, 118-126 (1912). 



18 E. Friedmann, Biochem. Z., 55, 436-442 (1913). 



" I. Smedley-MacLean and D. Hoffert, Biochem. J., 20, 343-357 (1926). 



