Exogenous pathway for lipid metabolism:

Lipid digestion and absorption
Lipids play an important role in cell structure and metabolism. TAGs are the major storage form of energy. Cholesterol is a component of cell membranes and precursor of steroid hormones. Lipid digestion occurs at lipid water interfaces since TAG is insoluble in water and digestive enzymes are water soluble. Lipids are digested and absorbed with the help of bile salts. Products of lipid digestion aggregate to form mixed micelles and are absorbed into the small intestine. Lipids are transported in the form of lipoproteins.

Endogenous pathway for lipid metabolism:

As discussed, CAHs result due to specific enzyme defects required for corticosteroid biosynthesis.

(the rate limiting setp in cholesterol biosynthesis.

Our results have interesting implications for evolution of enzymes for SQ biosynthesis. The pathway in bacteria begins with cyclopropanation of FPP to give PSPP. It is likely that PSPPase activity arose from ubiquitous chain elongation enzymes (PF00348) in the isoprenoid synthase superfamily. There is precedent for the independent emergence of cyclopropane-forming activity in chrysanthemyl diphosphate synthase from a FPPase in plants as recently as ∼50 million years ago (MYA). Eukaryotic SQase, which synthesizes PSPP from FPP in the absence of NADPH, also converts PSPP to HSQ. This observation, along with documented promiscuous activities for yeast SQase, supports a scenario for evolution of PSPPase from an ancestral chain elongation enzyme and of HSQase from PSPPase. In this scenario, the HSQ reductase activity in HpnE, which is a necessary step in the biosynthesis of hopanoid metabolites that insert properly into membrane, evolved independently from a protein in the flavin-dependent amino oxidase family.

statins block the pathway for synthesizing cholesterol in ..

There is a recent report of PSPPase activity in the colonial eukaryotic photosynthetic alga race B. has a gene for SQase (BSS) and three “SQase-like (SSL)” genes. The BSS protein converts FPP to SQ like other eukaryotic SQases. SSL1 converts FPP to PSPP, SSL2 catalyzes an NADPH-dependent reductive rearrangement/reduction of PSPP to SQ, and SSL3 catalyzes the NADPH-dependent reductive rearrangement of PSPP to botryococcene (BO), a triterpene isomer of SQ. SQ, BO, and their methylated derivatives are pumped into a translucent membrane surrounding individual cells in the colony, where they accumulate to 30–86% of the dry weight of the algal mass and provide flotation for maximal exposure of the organism to sunlight. BSS and the three SSL genes are estimated to have separated from a common ancestor ∼500 MYA. A brief phylogenetic analysis of the four genes places them firmly within a group of other eukaryotic SQase genes in fungi, plants, and animals (). Most likely, the PSPPase evolved from a eukaryotic SQase to facilitate regulation of the flux of FPP into sterol biosynthesis independently from the flux into biosynthesis of the massive amounts of methylated SQ and BO required for flotation. In contrast, in both Gram-positive and Gram-negative bacteria is distantly related to eukaryotic SQases, consistent with an ancient common ancestor for the bacterial and eukaryotic enzymes.


Cholesterol Biosynthesis from ..

Thatacidic lipid was later shown to be a universal component of photosynthetictissues.

Hirsch J reported the reversed-phase separation of non polar lipids on a columnof polymerized vegetable oil (Factice) ().

Klenk E et al.

is the terminal enzyme in the pathway of cholesterol biosynthesis

reported the reversed-phase separation of fatty acids by acomplex two-dimensional TLC employing a catalytic hydrogenationon the plate ().

First description of a direct titration method for analytical hydrogenation todetermine precisely the unsaturation of lipids ().

Discovery of O-amino acid (alanyl and lysyl) esters of phosphatidylglycerol in agram-positive bacteria ().

The first GLC analysis of natural triglycerides from milk fat was reported ().

Hematoside, the ganglioside of horse erythrocytes, is the first ganglioside(GM3) whose structure was elucidated ().

The complete structure of sulfatide (sulfated galactosylceramide) was elucidatedincluding the position of the sulfate group attached to the C3 of galactose ().

Methyl jasmonate was discovered in flowers of jasmine and was shown to be afragrant component in the essential oil from these flowers ().

Discovery of diether-type phospholipids in a an extremely halophilic bacteria () ().

First demonstration of the presence of 2-aminoethylphosphonic acid and itsglycerol ester in lipid extractsof the sea anemone, ().

Cholesterol biosynthesis and metabolism. - National …

demonstrated that acetylcholine is able to increasediglyceride levels in incubated pancreatic tissue ().

Inositol phosphorylceramide was shown to be a novel phospholipid in yeast ().

The first structure of a betain lipid (diacylglyceryl hydroxymethyltrimethylhomoserine) was reported in a vegetal ().

Wallen LL et al.

Cholesterol Biosynthesis – Atorvastatin

29-70).

The first component protein of an enzyme of fatty acid biosynthesis, fatty acidsynthase, was purified ().

Polyprenol diphosphates were shown to be involved in the biosynthesis ofpolysaccharides in () and in the biosynthesis of peptidoglycans in ().

The structure of juvenile hormone of insects was elucidated by Roller H ().

Cholesterol Biosynthesis: Lanosterol to Cholesterol - …

isolated digalactosyldiacylglycerol from human brain tissue ().

Diphosphatidylglycerol (cardiolipin) was definitively shown to be localizedexclusively to liver mitochondria (