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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Scheme 6 Biosynthesis of cholesterol from lanosterol.<br />

of the C-4 <strong>and</strong> C-14 methyl groups, <strong>and</strong> double-bond manipulation. Alkylation in<br />

the formation of plant sterols involves methylation at C-24 with S-adenosylmethionine<br />

to produce C28 sterols. The further methylation of a C-24 methylene substrate<br />

yields C-24 ethyl sterols. The details of the mechanism of demethylation <strong>and</strong> doublebond<br />

manipulation in plants are not clear, but it is highly likely to be very similar<br />

to that in animals. In plants, C-4 methyl groups are removed before the methyl group<br />

at C-14, whereas in animals it is the other way around. Sterols found in plants<br />

are very diversified. The structural features of major plant sterols are depicted in<br />

Figure 2.<br />

C. Regulation of Sterol Biosynthesis in Animals<br />

Sterol biosynthesis in mammalian systems has been intensely studied for several<br />

decades. Interest in the cholesterol biosynthesis pathway increased following clinical<br />

observations that the incidence of cardiovascular disease is greater in individuals<br />

with levels of serum cholesterol higher than average. More recently, the results of<br />

numerous clinical studies have indicated that lowering serum cholesterol levels may<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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