LIPID STORAGE UNDER ABNORMAL CONDITIONS 647 



der stated dietary and environmental conditions. These workers are of 

 the opinion that a comparison of lipotropic agents at any one dosage level 

 has no general applicability. 



e'. The Lipotropic Action of Proteins as Related to Their Amino Acid 

 Content: Although one would naturally suppose that the lipotropic 

 action of a protein would be the sum of the effects of the several amino acid 

 components, it may not always be the case. This relationship may not 

 even exist for a protein digest. Thus, Rose, Machella, and Gyorgy 633 re- 

 ported that methionine at a 50 mg. dosage (0.8% of the diet) did not pre- 

 vent the development of fatty livers in rats when a mixture of essential 

 fatty amino acids replaced the protein. Even when methionine consti- 

 tuted 2.4% of the diet, liver lipids were still at a level of 10% on the diet 

 containing the amino acid mixture. However, when choline chloride was 

 fed, the liver lipids were reduced to essentially normal values. 634 



Further reports indicate that the lipotropic action of proteins may not be 

 entirely dependent upon their methionine and cystine content. Thus, 

 Channon et al. 610 found that albumin, which contains more methionine than 

 does casein, had a lower lipotropic effect. Moreover, Best and Ridout 629 

 found that methionine and cystine, equivalent to that present in a 30% 

 casein diet, had a lower lipotropic action ; these latter results were directly 

 opposed to those of Tucker et al. 635 In their later work, Treadwell et al. 636 

 attributed the inferior lipotropic action of casein to the fact that the rats on 

 the higher level of protein grew better and thus had less methionine avail- 

 able to act as a lipotropic agent. Finally, Best and Ridout 629 reported that 

 methionine had a maximum lipotropic action at 0.5%; Channon and co- 

 workers 628 confirmed this result and reported that casein continued to exert 

 an increasing lipotropic activity up to 30%, which corresponded to a much 

 higher methionine level than the highest effective methionine dosage. 

 These results led Channon et al. 62S to postulate that "since methionine is 

 probably not the only lipotropic constituent of caseinogen, two possibilities 

 arise, either that some other amino acid also exerts a lipotropic action, or, 

 alternatively, added methionine is incapable of exerting its full action in the 

 absence of some other protein constituent." Although at the time there 

 was no direct evidence of the second possibility, the authors mention that 



633 C. S. Rose, T. E. Machella, and P. Gyorgy, Proc. Soc. Exptl. Biol. Med., 64, 352- 

 354 (1947). 



634 C. S. Rose, T. E. Machella, and P. Gyorgy, Proc. Soc. Exptl. Biol. Med., 67, 198-199 

 (1948). 



635 H. F. Tucker, C. R. Treadwell, and H. C. Eckstein, J". Biol. Chem., 135, 85-90 

 (1940). 



636 C. R. Treadwell, M. Groothuis, and H. C. Eckstein, J. Biol. Chem., 142, 653-658 

 (1942). 



