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- Sat Jan 04, 2003 12:11 pm
What are fatty acid binding proteins and what do they do?
|Dr. Safaa Mahmoud
- Tue Jan 07, 2003 12:56 pm
Lipids are organic compounds that are insoluble in water but soluble in ether, benzene or chloroform. They have important bilogical functions e.
g. component of the cell membrane structure.
Lipids are classified into simple lipids, conjugated and lipid derivatives.
Simple lipids are esters of fatty acids e.
Conjugated lipids are conjugates of lipids and another compound e.
Derived lipids are hydrolytic products of simple and conjugated lipids.
90% of alimentary fat are trigylecrides. Phospholipids and Cholesterol constitute the remaining 10%. The final digestive products of triglycerides are monoglyceride and fatty acids which are soluble in bile and form micelles which can traverse the intestinal mucosa cell membrane. Fatty acids are then transformed into acetyl CoA (CoAsh and ATP are required for the reaction). There are protiens called acyl carrier protiens that carry acyle group of the coressponding fatty acids.
Acetyl CoA is utilized for the formation of triglycerides. Triglycerides and Cholesterol esters form lipoprotein particle (a complex of apoprotien molecule and phospholipids). Lipoproteins are ableto traverse the intestinal lumen driving lipids into the circulation.
Lipoproteins are conjugated proteins and lipids that are important cellular compounds that act as lipid transporters. The central part of a lipoprotein molecule contains the triglyceride and Cholesterol ester while the surface is of apoprotiens, phospholipids, and Cholesterol.
Lipoproteins are divided into 4 main groups:
Chylomicrons which are lipoproteins that carry dietary Cholesterol and triglyceride from intestine to the liver and peripheral tissues respectively. To be secreted by intestinal cells a specific apolipoprotien called B48 mediate its binding to specific receptors.
VLDL (very low density lipoproteins) which transfer triglyceride from the liver to peripheral tissue. B100 mediates its secretion.
LDL which transfer Cholesterol from the liver to tissues and its excess preclude high risk for atherosclerosis and ischemic heart disease. B100 mediates its binding for cell receptors for endocytosis.
HDL which is the protective of atherosclerosis since it transfer Cholesterol from tissues back to the liver.
Lipoprotein lipase enable cells to uptake fatty acids from chylomicron and VLDL. Hormone sensitive lipase works during the lipolysis of stored triglycerides.
Fatty acids are stored in the adipose tissue in the form of triglyceride esters. Lipolyis is inhibited by Insulin(stimulate lipogenesis) and stimulated only during fasting and physical exercise by the effect of ant-Insulin hormones(adrenalin). Adrenalin stimulate B receptors to activate chain of reaction mediated by production of c-AMP and the activation of hormone sensitive lipase. Free fatty acid and monoglycerides are end products of this chain of reactions. Free fatty acids carried by Albumin, transported in the blood plasma to be used for energy production through B oxidation in the mitochondria of different tissues (skeletal ms and liver). Monoglycerides are transported to liver and enter the process of gluconeogenesis.
Transport of FA inside the mitochondria through the mitochondrial membrane is facilitated a protein called carnitine (carnitine shuttle).
Carnitine shuttle mechanism: FA are transformed to the corresponding acyle CoA in the cytosol by the aid of the enzyme CoA synthetase and ATP. At the external mitochondrail membrane carnitine is esterified by the aid of an enzyme called carnitine acyle transferase1 and acylcarnitine is formed. Along the internal mitochondrial membrane there is carnitine acylcarnitine translocase transport the complex into the mitochondria along the internal michochondrial membrane. By the action of another carnitine transferase 2 ; acyle CoA is released ready for B oxidation and carnitine is translocated through the membrane back.
Fatty acid synthesis occurs in the cytosol of liver, adipose tissue and occasionally in the mammary gland during lactation. During normal feeding fatty acids are formed from acetyl CoA derived by carbohydrate metabolism. Synthesis of fatty acids mandates the transfer of acyle from the mitochondria to the cell cytosol where they covalently bind to acyle carrier protein (ACP). Successive carboxylation of acetyl CoA leads to the formation of malonyl CoA, the main substrate of fatty acid chain synthesis.
Transport of FA to the cell cytosol is mediated by citrate shuttle: inside the mitochondria citrate is formed by the interaction between acetyl CoA and oxaloacetic acids by the aid of specific protein enzyme citrate synthetase. The conformational changes it makes by its two subunits, render the reaction products in accessible to water. They can then traverse the mitochondrial membrane to cytosol where acetyl CoA and oxaloacetic are released free to be used by the cell..
- Wed Oct 26, 2005 11:56 am
how do you test for coronary heart diesease, what are the usual symptoms and is it caused by human factors like excercise that we can control or other factors like family history thanks a lot
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