Biosynthesis of Cholesterol 



25 



the same figure is given the distribution of methyl and earboxyl carbons 

 of acetate in cholesterol, as it has been found by direct isolation. In 

 all cases the observed isotope distribution in cholesterol and that 

 postulated for squalene coincide. 



Squalene contains six isoprene units and each isoprene unit will 

 contain 3 methyl carbons and 2 earboxyl carbons of acetate, if syn- 



c 



o 



•C 



o 



O: ACETATE CH3 

 X-. ACETATE COOH 



CHOl£STEROL Cz? H46 



B 







y 



o 



c 



o 

 C 



c'" ^c^ 





C 

 o 



r^o^ 





I c ^ 



o 



SQUALENE C30 ^50 



Fig. 1. 



A. Distribution of acetate carbon found inlcholesterol. 



B. Postulated distributionTof acetate carbon in squalene. 



thesized by the mechanism postulated before. Squalene will therefore 

 contain six times as many methyl carbons and six times as many 

 earboxyl carbons, i.e. methyl carbons and earboxyl carbons of acetate 

 will be present in a ratio of 18:12. In the hypothetical conversion of 

 squalene to cholesterol, 3 branched carbon atoms must be lost, and the 

 ratio of methyl to earboxyl carbon atoms would, by the loss of 3 



