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lipoprotein lipase
Lipoprotein lipase (LPL) () is a member of the lipase gene family, which includes pancreatic lipase, hepatic lipase, and endothelial lipase. It is a water-soluble enzyme that hydrolyzes triglycerides in lipoproteins, such as those found in chylomicrons and very low-density lipoproteins (VLDL), into two free fatty acids and one monoacylglycerol molecule. It is also involved in promoting the cellular uptake of chylomicron remnants, cholesterol-rich lipoproteins, and free fatty acids. LPL requires ApoC-II as a cofactor.
LPL is attached to the luminal surface of endothelial cells in capillaries by the protein glycosylphosphatidylinositol HDL-binding protein 1 (GPIHBP1) and by heparin sulfated proteoglycans. It is most widely distributed in adipose, heart, and skeletal muscle tissue, as well as in lactating mammary glands.
==Synthesis==
In brief, LPL is secreted from parenchymal cells as a glycosylated homodimer, after which it is translocated through the extracellular matrix and across endothelial cells to the capillary lumen. After translation, the newly synthesized protein is glycosylated in the endoplasmic reticulum. The glycosylation sites of LPL are Asn-43, Asn-257, and Asn-359.〔 Glucosidases then remove terminal glucose residues; it was once believed that this glucose trimming is responsible for the conformational change needed for LPL to form homodimers and become catalytically active.〔〔 In the Golgi apparatus, the oligosaccharides are further altered to result in either two complex chains, or two complex and one high-mannose chain.〔〔 In the final protein, carbohydrates account for about 12% of the molecular mass (55-58 kDa).〔〔
Homodimerization is required before LPL can be secreted from cells.〔 After secretion, LPL is carried across endothelial cells and presented into the capillary lumen by the protein Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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