Lipoprotein metabolism Essay Example | Topics and Well Written Essays - 500 words

Lipoprotein metabolism - Essay Example This part accounts for the largest part of the cholesterol that is quantified as HDL-C in clinical laboratory. ÃŽ ±-HDLÂ  can be fractionated further by density into HDL3 and HDL2, by apolipoprotein composition and size. About 5-15% of apo A-1 in the human plasma is linked to pre–Î ²-electrophoretic mobility particles. This is further differentiated into pre–Î ²3-LpA-I, ÃŽ ²1-LpA-I and pre–Î ²2-LpA-I particles. These particles where reverse cholesterol transport occurs. This occurs in extravascular compartments. It is not clear where the HDL particles and pre–Î ²-electrophoretic mobility originates from. There are several mechanisms that have been proposed including cholesteryl ester transfer protein (CETP), direct interaction between cell membrane and free apolipoproteins, hepatic lipase (HL), release during the HDL interconversion by phospholipid transfer protein (PLTP) and direct secretion from enterocytes into plasma. High-density lipoprotein is produced in the intestine and liver. It plays a key role in the reverse cholesterol transport. By accepting free cholesterol from the peripheral tissues, HDL lowers the blood cholesterol levels. HDL exchanges lipids and proteins with other lipoproteins. It donates apoproteins E and C11 to nascent VLDL’s. HDL also produces a paraoxonase enzyme. This enzyme inhibits the oxidation of low-density lipoprotein. The HDL precursor particles can also absorb free cholesterol from the cell membrane in a process mediated by apoA-1, ApoA-IV and ATP binding cassette transporter 1. ApoA-1 is the HDL’s major apolipoprotein. It activates the cholesterol acyltransferase (LCAT) (a lecithin enzyme) that esterifies the free accepted cholesterol to increase the efficiency of cholesterol packaging for transport. By acquisition of additional esters, triglycerides, and apolipoproteins, the particles of HDL3 are transformed into HDL2 particles which are relatively la rger. By estension, HDL plays a role in transferring the