644 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



and Eckstein, 611 lipotropic activity parallels the methionine content as re- 

 ported for proteins by Baernstein. 612 The lack of potency exhibited by 

 arachin, and the low potency reported for gelatin, were later shown to be 

 traceable to their low methionine contents. On the other hand, Sauber- 

 lich 613 reported that the supplementation of a 7% casein diet with 10% of 

 zein, lactalbumin, or casein prevented the development of fatty livers in 

 rats, while 10% gelatin was also partially effective. Harper et al. 6UM5 

 likewise noted that the addition of 6% gelatin to the diet reduced the ac- 

 cumulation of liver fat in rats. 



d'. The Lipotropic Action of Amino Acids: The explanation for the 

 lipotropic action of protein is now known to reside in the amino acids of 

 which they are composed. There are three categories to which these amino 

 acids may be assigned. 



(a') Amino Acids Having No Lipogenic or Lipotropic Action: In the 

 first group, the amino acids are completely inactive in producing fatty 

 livers or in preventing the accumulation of fat in the liver. Thus, Beeston 

 and Channon 616 reported that aspartic acid, glutamic acid, glycine, lysine, 

 phenylalanine, and serine were ineffective in influencing liver fat deposition. 

 Beeston and co-workers 617 - 618 found that alanine, arginine, histidine, hy- 

 droxyproline, leucine, proline, and valine were likewise inactive, and con- 

 firmed the fact that aspartic acid and lysine belong in this category. Ty- 

 rosine was found to have some effect in preventing glyceride deposition. 618 

 The inactivity, from a lipotropic standpoint, of DL-leucineandDL-valinewas 

 confirmed by Singal and Eckstein, 619 who demonstrated that djenkolic acid 

 and Z)L-isoleucine behave likewise. In a later study of fourteen pure amino 

 acids, Channon and co-workers 620 revised their earlier conclusions to include 

 tyrosine as a possible lipotropic agent acting on fatty livers containing fat 

 or cholesterol. There was some evidence, also, that tryptophane may pos- 

 sess a slight lipotropic action. On the other hand, Eckstein 621 was unable 

 to demonstrate lipotropic effects on the part of any essential amino acids 

 other than methionine. 



611 H. F. Tucker and H. C. Eckstein, J. Biol. Chem., 121, 479-484 (1937). 



612 H. D. Baernstein, J. Biol. Chem., 97, 669-674 (1932); 115, 25-32 (1936). 



613 H. E. Sauberlich, Federation Proc, 12, 263 (1953). 



614 A. E. Harper, W. J. Monson, D. A. Benton, and C. A. Elvehjem, J. Nutrition, 50, 

 383-393 (1953). 



615 A. E. Harper, W. J. Monson, D. A. Benton, and C. A. Elvehjem, Federation Proc, 

 12, 416 (1953). 



616 A. W. Beeston and H. J. Channon, Biochem. J., 30, 280-284 (1936). 



617 A. W. Beeston and A. P. Piatt, J. Soc. Chem. Ind., 58, 557 (1939). 



618 A. W. Beeston, H. J. Channon, and A. P. Piatt, J. Soc. Chem. Ind., 56, 292 (1937). 



619 S. A. Singal and H. C. Eckstein, /. Biol. Chem., 140, 27-34 (1941). 



620 H. J. Channon, G. T. Mills, and A. P. Piatt, Biochem. J., 37, 483-492 (1943). 



