378 VIII. CHOLESTEROL AND RELATED STEROLS 



of conversion to cholesterol. Dam^^^ demonstrated that the tissues of 

 chicks raised on cholesterol-low diets contained more of this sterol than 

 could be accounted for in their food and in the eggs from which they had 

 been hatched. The cholesterol unaccounted for could only have originated 

 synthetically. Imhauser'®^ like^vise proved the synthesis of cholesterol in 

 a human subject; he was able to demonstrate more cholesterol in the feces 

 than in the food ingested. Moreover, Schoenheimer and Breusch^^* re- 

 ported that, when mice were fed on a bread diet, which is practically de- 

 void of cholesterol, the animals synthesized as much cholesterol in one 

 month as they had initially contained. More recently, cholesterol syn- 

 thesis has again been demonstrated in man by the use of the so-called 

 balance type of experiments. The extent of cholesterol synthesis in man, 

 as judged by the amount of the negative balance on cholesterol-free diets, 

 was calculated by Frazer^^^ as 300 mg. per day, based upon the data of 

 Channon,^^^ Schoenheimer and Breusch,'^"* and of Gardner and Gains- 

 borough.^® 



Somewhat later, the synthesis of cholesterol in the animal body was 

 proved by the use of isotopic tracers. Thus, Rittenberg and Schoen- 

 heimer^*^ interpreted their demonstration of the incorporation of deute- 

 rium into cholesterol in mice as evidence of the synthesis of this sterol; 

 in fact, they suggest that it is formed "by the coupling of a large number of 

 small molecules." It is now known that CoA functions in this reaction. 



a. The Inability of Insects to Synthesize Cholesterol. In spite of the 

 fact that the higher animals, without exception, have the capacity to syn- 

 thesize cholesterol, this ability is not universal throughout the animal 

 kingdom. Thus, a nmnber of larvae, parasites, and insects require 

 cholesterol or other related sterols as dietary essentials, inasmuch as they 

 are unable to synthesize the steroid nucleus. 



Fraenkel and co-workers^** were the first to call attention to the fact that 

 the larvae of the scavenger beetle (Dermestes vulpinus) will grow only if 

 the food contains a sterol. The sterols which supply this requirement in- 

 clude purified cholesterol, cholesteryl acetate, 7-dehydrocholesterol, and 

 7-dehydrocholesteryl monobenzoate. The following sterols were shown 



1" H. Dam, Biochem. Z., 220, 158-163 (1930). 

 1" K. Imhauser, Klin. Wochschr., 9, 71-72 (1930). 



1" R. Schoenheimer and F. Breusch, /. Biol. Chem., 103, 439-448 (1933). 

 1^^ A. C. Frazer, Lipid Metabolism, in G. H. Bourne and G. W. Kidder, Biochemistry 

 and Physiology of Nutrition, vol. I, Academic Press, New York, 1953, pp. 212-264. 



166 H. J. Channon, Biochem. J., 19, 424-432 (1925). 



167 D. Rittenberg and R. Schoenheimer, /. Biol. Chem., 121, 235-253 (1937). 



168 G. Fraenkel, J. A. Reid, and M. Blewett, Biochem. J., 35, 712-720 (1941). 



