Biosynthesis Of Cholesterol

A. General Comments

The most commonly occurring steroid is cholesterol (3). Cholesterol is present in practically all living organisms, including blue-green algae and bacteria. The levels of cholesterol in plant tissues are low, except in some pollen and seed oil. Animal products are rich sources of cholesterol; cholesterol is present in high concentrations in the myelin sheath and in almost pure form in gallstones. Above-average levels can be found in skin, sperm cells, and egg yolk. Virtually all cell membranes in higher animals include cholesterol as an integral component.

A range of 180-260 mg of total cholesterol per 100 m of serum is generally accepted as the normal level for the American adult. Although there is little esterified cholesterol in the peripheral tissues, 70-75% of the cholesterol of plasma is esterified.

Most organisms have an enzymatic capability to biosynthesize cholesterol. Notable exceptions include protozoa, fungi, arthropods, annelids, mollusks, sea urchins, and sharks. However, many organisms will incorporate cholesterol into their cellular membrane if it is provided as a dietary source. In mammalian tissues the principal sites of production of cholesterol are the skin, liver, and intestinal mucosa; measurable biosyn-thetic activity is also found in lung, kidney, adrenal, gonad, muscle, brain, and adipose tissue.

B. Pathway of Production

Because cholesterol is the precursor of the seven classes of steroids summarized in Table 2-1, it is useful to consider the biosynthetic pathway of production of cholesterol. The pioneering work of R. Schoenheimer, D. R. Rittenburg, and K. Bloch established that all 27 carbons of cholesterol are derived from acetate. In this remarkable biosynthetic process, 18 molecules of acetate are processed by at least 27 enzymes to produce the final product, cholesterol. The sources of all the carbon atoms of cholesterol in relation to the carboxyl

Androst-4-ene-3,17-dione (25)

Androst-4-ene-3,17-dione (25)

5a-Androstane-3,17-dione (26)

Was this article helpful?

0 0
Get Rid of Gallstones Naturally

Get Rid of Gallstones Naturally

One of the main home remedies that you need to follow to prevent gallstones is a healthy lifestyle. You need to maintain a healthy body weight to prevent gallstones. The following are the best home remedies that will help you to treat and prevent gallstones.

Get My Free Ebook

Post a comment