Lipoprotein lipase (LPL) (EC 3.1.1.34, systematic name triacylglycerol acylhydrolase (lipoprotein-dependent)) 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:
Apolipoproteins are proteins that bind lipids to form lipoproteins. They transport lipids in blood, cerebrospinal fluid and lymph.
Apolipoprotein E (Apo-E) is a protein involved in the metabolism of fats in the body of mammals. A subtype is implicated in Alzheimer's disease and cardiovascular diseases. It is encoded in humans by the gene APOE.
Apolipoprotein B (ApoB) is a protein that in humans is encoded by the APOB gene. Its measurement is commonly used to detect risk of atherosclerotic cardiovascular disease.
Apolipoprotein C-II, or apolipoprotein C2 is a protein that in humans is encoded by the APOC2 gene.
Apolipoprotein C-I is a protein component of lipoproteins that in humans is encoded by the APOC1 gene.
Lecithin–cholesterol acyltransferase is an enzyme found in many animals, including humans. It converts free cholesterol into cholesteryl ester, a more hydrophobic form of cholesterol. This process sequesters cholesterol ester into the core of a lipoprotein particle, eventually making the newly synthesized HDL spherical and forcing the reaction to become unidirectional since the particles are removed from the surface. The enzyme is bound to high-density lipoproteins (HDLs) (alpha-LCAT) and LDLs (beta-LCAT) in the blood plasma. LCAT deficiency can cause impaired vision due to cholesterol corneal opacities, anemia, and kidney damage. It belongs to the family of phospholipid:diacylglycerol acyltransferases.
Apolipoprotein AI(Apo-AI) is a protein that in humans is encoded by the APOA1 gene. As the major component of high-density lipoprotein (HDL) particles, it has a specific role in lipid metabolism.
Apolipoprotein C-III also known as apo-CIII, and apolipoprotein C3, is a protein that in humans is encoded by the APOC3 gene. Apo-CIII is secreted by the liver as well as the small intestine, and is found on triglyceride-rich lipoproteins such as chylomicrons, very low density lipoprotein (VLDL), and remnant cholesterol.
Apolipoprotein C-IV, also known as apolipoprotein C4, is a protein that in humans is encoded by the APOC4 gene.
Apolipoprotein D (ApoD) is a protein that in humans is encoded by the APOD gene. Unlike other lipoproteins, which are mainly produced in the liver, apolipoprotein D is mainly produced in the brain and testes. It is a 29 kDa glycoprotein discovered in 1963 as a component of the high-density lipoprotein (HDL) fraction of human plasma. It is the major component of human mammary cyst fluid. The human gene encoding it was cloned in 1986 and the deduced protein sequence revealed that ApoD is a member of the lipocalin family, small hydrophobic molecule transporters. ApoD is 169 amino acids long, including a secretion peptide signal of 20 amino acids. It contains two glycosylation sites and the molecular weight of the mature protein varies from 20 to 32 kDa.
Sterol regulatory element-binding protein cleavage-activating protein, also known as SREBP cleavage-activating protein or SCAP, is a protein that in humans is encoded by the SCAP gene.
Hepatic lipase (HL), also called hepatic triglyceride lipase (HTGL) or LIPC (for "lipase, hepatic"), is a form of lipase, catalyzing the hydrolysis of triacylglyceride. Hepatic lipase is coded by chromosome 15 and its gene is also often referred to as HTGL or LIPC. Hepatic lipase is expressed mainly in liver cells, known as hepatocytes, and endothelial cells of the liver. The hepatic lipase can either remain attached to the liver or can unbind from the liver endothelial cells and is free to enter the body's circulation system. When bound on the endothelial cells of the liver, it is often found bound to heparan sulfate proteoglycans (HSPG), keeping HL inactive and unable to bind to HDL (high-density lipoprotein) or IDL (intermediate-density lipoprotein). When it is free in the bloodstream, however, it is found associated with HDL to maintain it inactive. This is because the triacylglycerides in HDL serve as a substrate, but the lipoprotein contains proteins around the triacylglycerides that can prevent the triacylglycerides from being broken down by HL.
Apolipoprotein A-IV is plasma protein that is the product of the human gene APOA4.
Phospholipid transfer protein is a protein that in humans is encoded by the PLTP gene.
Microsomal triglyceride transfer protein large subunit is a protein that in humans is encoded by the MTTP, also known as MTP, gene.
Apolipoprotein B mRNA editing enzyme, catalytic polypeptide 1 also known as C->U-editing enzyme APOBEC-1 is a protein that in humans is encoded by the APOBEC1 gene.
Vigilin is a 110 kDa protein that in humans is encoded by the HDLBP gene.
Apolipoprotein M is an apolipoprotein and member of the lipocalin protein family that in humans is encoded by the APOM gene. It is found associated with high density lipoproteins and to a lesser extent with low density lipoproteins and triglyceride-rich lipoproteins. The encoded protein is secreted through the plasma membrane but remains membrane-bound, where it is involved in lipid transport. Two transcript variants encoding two different isoforms have been found for this gene, but only one of them has been fully characterized. It lacks an external amphipathic motif and is uniquely secreted to plasma without cleavage of its terminal signal peptide. The average molecular weight is 21253 Da, and the monoisotopic molecular weight is 21239 Da.
Apolipoprotein F is a protein that in humans is encoded for by the APOF gene. The product of this gene is one of the minor apolipoproteins found in plasma. This protein forms complexes with lipoproteins and may be involved in transport and/or esterification of cholesterol.
