FAT METABOLISM 739 



Embden's experiments are equally convincing. He studied the forma- 

 tion of acetone in defibrinated blood perfused through the freshly excised 

 liver. Normally only a trace of this substance is formed, but when fatty 

 acids with an even number of carbon atoms were added to the blood, 

 they gave rise to a marked increase in acetone, whereas those with an 

 uneven chain failed to cause any change. The acetone was found to be 

 derived immediately from acetoacetic acid. The following table shows 

 the results. 



NORMAL FATTY ACID FORMATION OF 



ACETOACETIC ACID 



Acetic acid CH 3 .COOH 



Propionic acid CH 3 .CH 2 .COOH 



Butyric acid CH 3 . CH 2 . CH 2 . COOH + 



Valeric acid CH 3 . CH 2 . CH 2 . CH 2 . COOH 



Caproic acid CH 3 . CH 2 . CH 2 . CH 2 . CH, . COOH + 



Heptylic acid CH 3 . CH, . CH 2 . CH 2 . CH 2 . CH, . COOH 



Octoic acid CH 3 . CH" 2 . CH 2 . CH, . CH, . CH', . CH 2 . COOH + 



Nonoic acid CH 3 . CH 2 . CH 2 . CH, . CH 2 . CH 2 . CH 2 . CH 2 . COOH 



Decoie acid GH 3 . GH 2 . CH 2 . CH 2 '. CH 2 . CH 2 ". CH 2 . CH 2 . CH 2 . CH 2 . COOH + 



(From Dakin.) 



For a long time it was difficult for chemists to understand how such 

 a process of oxidation at the /3-C-atom could occur, since they were 

 unable to bring it about in the laboratory by the use of the ordinary 

 oxidizing agents, but recently Dakin has removed the difficulty by show- 

 ing that hydrogen peroxide (H 2 2 ) oxidizes fatty acids just exactly in 

 this way. 



We may sum up the results of these experiments and observations by 

 stating that normal saturated fatty acids and their phenyl derivatives can 

 undergo oxidation, not only in the animal body, but also in vitro y in such 

 a manner that the two (or some multiple thereof) terminal C-atom\s are 

 removed at each successive step in their decomposition. 



But we must not be too hasty in concluding from these experiments that the steps 

 in the process are necessarily in the order of first, the production of a /3-hydroxy acid, 

 and second the oxidation of this to a Ketone group. The mere presence, side by side, 

 of j3-hydroxy butyric acid and of acetone in the above experiments does not indicate 

 which is the antecedent of the other, and indeed there are several experimental facts 

 that seem to show that the hydroxy acid may be derived from the ketone. For example 

 when acetoacetic acid is added to minced liver and the mixture incubated, 0-hydroxy- 

 butyric acid is formed (a reduction process), although less usually the reverse action 

 (oxidation) may occur when /3-hydrqxy acid is added. A reversible reaction must there- 

 fore be capable of occurring between these two substances, thus: 



reduction 



CH 3 .CHOH.CH 2 .COOH < - CH 3 .CO.CH,.COOH. 



oxidation 

 (/3-oxybutyric acid) > (acetoacetic acid) 



