LIPID STORAGE UNDER ABNORMAL CONDITIONS 645 



(&') Amino Acids Having Lipogenic (Antilipotropic) Action: The 

 second category in classifying amino acids as to their action in regard to 

 liver lipids includes those which tend to increase the level of liver fats. 

 These are classed as lipogenic or antilipotropic agents. Curtis and New- 

 burgh 622 reported, as early as 1927, that cystine possesses this property. 

 This observation was confirmed by Beeston and Channon, 616 who demon- 

 strated that, when an amount of cystine as small as 0.2% was added to a diet 

 containing 5% of casein and 40% of fat, the content of liver fat was 

 doubled. When the casein content of the diet was increased to 30%, the 

 antilipotropic effect of cystine was abolished. Tucker and Eckstein 611 con- 

 firmed the antilipotropic effect of cystine, while Singal and Eckstein 609 

 demonstrated, several years later, with mice, that cysteine, HSCH 2 CH- 

 (NH 2 )COOH, and homocystine, HOOCCH(NH 2 )CH,CH 2 S— SCH 2 CH 2 - 

 CH(NH 2 )COOH, were antilipotropic. Salmon 623 likewise demonstrated 

 that the deficiency of labile methyl groups in diets containing less than 18% 

 of casein was accentuated by the feeding of cystine alone or with fat. 

 Griffith, 624 as well as Griffith and Mulford, 625 ascribed the antilipotropic 

 action of cystine to the increased choline requirements due to a general im- 

 provement in the nutritional state. Associated with this is the augmented 

 demand for methionine to be used for protein synthesis, which diverts a 

 considerable amount of this amino acid from acting as a lipotropic agent. 

 Smythe 626 ascribed this antilipotropic action of cystine to the toxic action of 

 H 2 S liberated as a result of the metabolism of cystine. 



However, Stetten and Salcedo 433 concluded that cystine actually in- 

 creases fat formation in the animal body. When deuterium was given to 

 rats on a choline-free diet, deuterio-fats were found only in the liver. Under 

 such conditions there is a blocking of the passage of fat from this organ to 

 the tissues. On the other hand, when cystine was administered, the deu- 

 terium was found in depot fat as well as in liver fat. This result is inter- 

 preted as proving that cystine promotes fat formation. 



(c') Amino Acids Having Lipotropic Action : The most important cate- 

 gory of amino acids which influence the level of liver lipids is the third one, 

 which includes only methionine, CH 3 SCH 2 CH 2 CH(NH 2 )COOH. Tucker 

 and Eckstein made the brilliant discovery that methionine is lipotropic. 611 

 These workers suggested that the lipotropic action of casein — and pre- 



621 H. C. Eckstein, J. Biol. Chem., 195, 167-174 (1952). 



622 A. C. Curtis and L. H. Newburgh, Arch. Internal Med., 39, 828-832 (1927). 



623 W. D. Salmon, /. Nutrition, 33, 155-168 (1947). 



624 W. H. Griffith, /. Nutrition, 21, 291-306 (1941). 



626 W. H. Griffith and D. J. Mulford, J. Nutrition, 21, 633-646 (1941). 

 626 C. V. Smythe, /. Biol. Chem., 142, 387-400 (1942). 



