BIOSYNTHESIS OF CHOLESTEROL 379 



to be inactive : sitosterol, ergosterol, 7-hydroxycholesteryl dibenzoate, and 

 calciferol. The minimum quantity necessary for satisfactory growth 

 varied with the sterol, being 1 mg./3 g. food for cholesterol and 7-dehydro- 

 cholesteryl monobenzoate, and less than 0.5 mg./3 g. food for 7-dehydro- 

 cholesterol. 



The larvae of the common vinegar fly, or fruit fly (Drosophila melano- 

 gaster), were likewise found by van't Hoog^^^ to require sterols, but they were 

 less selective. According to this latter worker, the following sterols all 

 served satisfactorily to supply the required component: cholesterol, si- 

 tosterol, stigmasterol, ergosterol, phytosterol, cholestanol (dihydrocholes- 

 terol) and cholestenone. 



In a study of the larvae of the black carpet beetle {Attagenus piceus), 

 McKennis^^° demonstrated that some larvae can use either plant or animal 

 sterols while others, such as A. piceus, respond only to the animal sterols; 

 thus, cholesterol was active (even when highly purified), while synthetic 7- 

 hydroxycholesterol and 7-ketocholesterol did not support growth. How- 

 ever, cholesterol dibromide did possess activity. 



Fraenkel and Blewett^^' observed that the presence of one per cent of 

 cholesterol in the diet improved the growth of a number of insects normally 

 living on flour. In the absence of cholesterol, the growth was impaired 

 somewhat in the case of Tribolium confusum Duv. ("confused" brown flour 

 beetle), Silvanus (Oryzaephilus) surinamensis (saw-toothed grain beetle) 

 and Lasioderma serricorne Fabr. (cigarette beetle), while it was appreciably 

 or severely impaired in the case of Ptinus tectus Boield (brown spider bee- 

 tle), Sitodrepa panicea L. ("drug-store" beetle) and Ephestia kuehniella 

 Zell. (Mediterranean flour moth). When an aqueous yeast extract was 

 supplied in place of yeast and cholesterol, all the insects were found to de- 

 velop, although at a reduced rate. The retardation resulted from a defi- 

 ciency of biotin, which is contained in the insoluble portion of the yeast. 

 In a later report by Fraenkel and Blewett,^^^ it was noted that 7-dehydro- 

 cholesterol, as well as cholesterol or sitosterol with only one double bond in 

 ring B, could be used as a source of sterol. However, when ring B was rup- 

 tured, as in vitamin Do, the resulting compound was unsatisfactory, be- 

 cause the tetracyclic arrangement had been changed. The nutritional 

 value of cholesterol was likewise destroyed by the following structm*al 

 changes in the molecule: loss of the secondary alcohol group (A^-choles- 



1" E. G. van't Hoog, Z. Vitaminforsch., 5, 118-126 (1936). 



i'« H. McKennis, Jr., /. Biol. Chem., 167, 645-654 (1947). 



"1 G. Fraenkel and M. Blewett, /. Exptl. Biol, 20, 28-34 (1943). 



'" G. Fraenkel and M. Blewett, Biochem. J., 37, 692-695 (1943). 



