Biosynthesis of cholesterol and steroids

The conversion of HMG-CoA to mevalonate by HMG-CoA reductase is the rate-limiting step of cholesterol biosynthesis and is under strict regulatory control (see Figure 1 ). HMGR is the target of compounds that are effective in lowering serum cholesterol levels. Human HMG-CoA reductase consists of a single polypeptide chain of 888 amino acids. The amino-terminal residues are membrane bound and reside in the endoplasmic reticulum membrane, while the catalytic site of the protein resides in its cytoplasmic, soluble carboxy-terminal portion. A linker region connects the two portions of the protein.

From a dietary perspective, plant cells do not manufacture cholesterol, and it is not found in plant foods. [30] [32] Some plant foods, such as avocado , flax seeds and peanuts , contain phytosterols , which compete with cholesterol for absorption in the intestines, reducing the absorption of both dietary and bile cholesterol. [33] However, a typical diet contributes on the order of grams of phytosterols, which is not enough to have a significant impact on blocking cholesterol absorption. Phytosterols intake can be supplemented through the use of phytosterol-containing functional foods or dietary supplements that are recognized as having potential to reduce levels of LDL -cholesterol. [34] Some supplemental guidelines have recommended doses of phytosterols in the – grams per day range (Health Canada, EFSA, ATP III, FDA). A recent meta-analysis demonstrating a 12% reduction in LDL-cholesterol at a mean dose of  grams per day. [35] However, the benefits of a diet supplemented with phytosterols have been questioned. [36]

Biosynthesis of cholesterol and steroids

biosynthesis of cholesterol and steroids

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