Application

Lipoprotein, low density from human plasma has been used:as an additive in cholesterol-free RPMI mediaas a component in buffer to perform an assayfor measuring lipid peroxidationto stimulate hepatic macrophagesas a plasma protein to determine pazopanibunbound fraction (fu%) by equilibrium dialysis

Biochem/physiol Actions

LDL and HDL transport both dietary and endogenous cholesterol in the plasma. LDL is the main transporter of cholesterol and cholesteryl esters and makes up more than half of the total lipoprotein in plasma. LDL is absorbed by the liver and other tissues via receptor mediated endocytosis. The cytoplasmic domain of the LDL receptor facilitates the formation of coated pits; receptor-rich regions of the membrane. The ligand binding domain of the receptor recognizes apo-B100 on LDL, resulting in the formation of a clathrin-coated vesicle. ATP-dependent proton pumps lower the pH inside the vesicle resulting dissociation of LDL from its receptor. After loss of the clathrin coat the vesicles fuse with lysozomes, resulting in peptide and cholesteryl ester enzymatic hydrolysis. The LDL receptor can be recycled to the cell membrane. Insulin, tri-iodothyronine and dexamethasome have shown to be involved with the regulation of LDL receptor mediated uptake.

Caution

Freezing of lipoprotein solutions may cause structural or compositional changes.

Other Notes

View more information on lipoprotein function and lipid transport at www.sigma-aldrich.com/enzymeexplorer

Physical form

Solution in 150 mM NaCl and 0.01% EDTA, pH 7.4

Physical properties

Low density lipoproteins are smaller than VLDL and IDL (26 nm) (MW approximately 3.5 million) and more dense (~1.04). The protein component of LDL is apolipoprotein B100. LDL contains 20-22% protein, 10-15% triglycerides, 20-28% phospholipids, 37-48% cholesteryl esters and 8-10% cholesterol.