22 



Samuel Gurin and Roscoe O. Brady 



can be explained on the basis of its ready conversion to aceto- 

 acetate as well as to acetate. It is of interest that incubation 

 of liver slices with labelled acetate in the presence of non- 

 radioactive isovalerate fails to stimulate the incorporation of 

 ^*C acetate into cholesterol. If the synthesis of isopropyl 

 fragments is required for this biosynthesis, it is not a limiting- 

 reaction. 



Although hepatic biosynthesis of long chain fatty acids from 

 two-carbon fragments or other precursors is practically 



CHOLESTEROL 



Fig. 1. Metabolic interrelations of lipids in liver. 



abolished in alloxanized rats and depancreatized cats, liver 

 slices obtained from such animals retain their ability to syn- 

 thesize cholesterol at a normal or perhaps accelerated rate 

 (Brady and Gurin, 19506). It was suggested, at the same 

 time, that the synthesis of fatty acids in the liver proceeds 

 by a process independent of fatty acid breakdown (Fig. 1). 

 In the diabetic state, the synthetic process is blocked, hence 

 the accumulation of fat in such livers cannot be ascribed to 

 hepatic synthesis. Since surviving liver tissue obtained from 

 Houssay cats (Brady, Lukens and Gurin, 1951a) is capable 

 of incorporating labelled acetate into long chain fatty acids 



