SOURCES OF FAT IN ANIMAL BODY 543 



condensation to form hydroxybutyral. This condensation product is re- 

 duced to butyraldehyde ; successive condensations of acetaldehyde with 

 the new fatty aldehyde occur, followed by a reduction of the subsequent B- 

 hydroxyl groups. When the chain has reached the desired length, oxida- 

 tion of the terminal aldehyde group to an acid group occurs, yielding the 

 typical fatty acids present in animal fats. These fatty acids can combine 

 with glycerol (which is readily produced from glucose) to form the neutral 

 fat. 



Although there is little direct evidence that acetaldehyde may serve as 

 the building stone for fatty acids, it is known to be a physiological com- 

 pound, and has been reported to be a component of urine. 126 An especially 

 compelling argument for acetaldehyde as an intermediate is the important 

 role of pyruvic acid in fat synthesis. Considerable amounts of pyruvic acid 

 are present in the organism whenever carbohydrate metabolism is pro- 

 ceeding at a high rate. Neuberg and Karczag 127 have proved that pyruvic 

 acid is normally converted to acetaldehyde as a result of the action of the 

 enzyme, carboxylase. It is now known that a coenzyme is also required, 

 which is referred to as co-carboxylase. The coenzyme has been identified 

 as thiamine pyrophosphate. A similar reaction occurs in vivo, as is indi- 

 cated by the fact that, when the breakdown of pyruvic acid is prevented by 

 the absence of the coenzyme, as is the case in thiamine deficiency, an ac- 

 cumulation of pyruvic acid in the blood can be demonstrated, both di- 

 rectly 128 and indirectly, as implied from the urinary pyruvate, especially 

 when carbohydrate is ingested. 129 - 130 Since it has also been found that 

 thiamine is necessary for fat synthesis, 123,131—133 one ma y we j] assiime that 

 thiamine acts in this capacit}^ by allowing the reaction, pyruvic acid — > 

 acetaldehyde to proceed in a normal manner. By a priori reasoning, one 

 may therefore conclude that acetaldehyde is the essential intermediate in 

 the synthesis of fat. On the other hand, Quackenbush and associates 134 

 reported that other B vitamins, in addition to thiamine, are equally con- 

 cerned with the fat synthesis reaction. 



Additional proof that thiamine is related to fat synthesis is to be found 



126 W. Stepp and R. Feulgen, Z. physiol. Chem., 119, 72-75 (1922). 



127 C. Neuberg and L. Karczag, Biochem. Z., 36, 68-75 (1911). 



128 R. H. S. Thompson and R. E. Johnson, Biochem. J., 29, 694-700 (1935). 



129 H. A. Harper and H. J. Deuel, Jr., J. Biol. Chem., 137, 233-238 (1941). 



130 M. E. Shils, H. G. Day, and E. V. McCoIlum, /. Biol. Chem., 139, 145-161 (1941). 



131 D. V. Whipple and C. F. Church, J. Biol. Chem., 11 4, cvii-cviii (1936). 



132 E. W. McHenry, Science, 86, 200 (1937). 



133 E. W. McHenry and G. Gavin, J. Biol. Chem., 125, 653-660 (1938). 



134 F. W. Quackenbush, H. Steenbock, and B. R. Platz, J. Biol. Chem., 145, 163-167 

 (1942). 



