Protein high-density lipoprotein

Cholesterol is biosynthesized in the liver trans ported throughout the body to be used in a va riety of ways and returned to the liver where it serves as the biosynthetic precursor to other steroids But cholesterol is a lipid and isn t soluble in water How can it move through the blood if it doesn t dis solve in if The answer is that it doesn t dissolve but IS instead carried through the blood and tissues as part of a lipoprotein (lipid + protein = lipoprotein) The proteins that carry cholesterol from the liver are called low density lipoproteins or LDLs those that return it to the liver are the high-density lipoproteins or HDLs If too much cholesterol is being transported by LDL or too little by HDL the extra cholesterol builds up on the walls of the arteries caus mg atherosclerosis A thorough physical examination nowadays measures not only total cholesterol con centration but also the distribution between LDL and HDL cholesterol An elevated level of LDL cholesterol IS a risk factor for heart disease LDL cholesterol is bad cholesterol HDLs on the other hand remove excess cholesterol and are protective HDL cholesterol IS good cholesterol... 

Heterogeneous reaction (Section 6 1) A reaction involving two or more substances present in different phases Hydro genation of alkenes is a heterogeneous reaction that takes place on the surface of an insoluble metal catalyst Heterolytic cleavage (Section 4 16) Dissociation of a two electron covalent bond in such a way that both electrons are retained by one of the initially bonded atoms Hexose (Section 25 4) A carbohydrate with six carbon atoms High density lipoprotein (HDL) (Section 26 11) A protein that carries cholesterol from the tissues to the liver where it is metabolized HDL is often called good cholesterol Histones (Section 28 9) Proteins that are associated with DNA in nucleosomes... 

High-density lipoproteins (HDL) have much longer life spans in the body (5 to 6 days) than other lipoproteins. Newly formed HDL contains virtually no cholesterol ester. However, over time, cholesterol esters are accumulated through the action of lecithin cholesterol acyltransferase (LCAT), a 59-kD glycoprotein associated with HDLs. Another associated protein, cholesterol ester transfer protein, transfers some of these esters to VLDL and LDL. Alternatively, HDLs function to return cholesterol and cholesterol esters to the liver. This latter process apparently explains the correlation between high HDL levels and reduced risk of cardiovascular disease. (High LDL levels, on the other hand, are correlated with an increased risk of coronary artery and cardiovascular disease.)... 

Abbtvviations apoC-lll, apolipoprotein C-lll apoA-l, apolipoprotein A-l apoA-ll, apolipoprotein A-ll CRP, C-reactive protein VLDL, very low density lipoprotein TG, triglycerides LDL-C, low density lipoprotein cholesterol HDL-C, high density lipoprotein cholesterol. 

Heparin Sulfate Proteoglycans Hepatic Lipase Hepatitis Hepatitis C Heptahelical Domain Heptahelical Receptors HERG-channels Heterologous Desensitization Heterologous Expression System Heterotrimeric G-Proteins Hidden Markov Model High-density Lipoprotein (HDL)... 

Figure 25-3. Metabolic fate of chylomicrons. (A, apolipoprotein A B-48, apolipoprotein B-48 , apolipoprotein C E, apolipoprotein E HDL, high-density lipoprotein TG, triacylgiycerol C, cholesterol and cholesteryl ester P, phospholipid HL, hepatic lipase LRP, LDL receptor-reiated protein.) Only the predominant lipids are shown.

FIGURE 3.2.2 Metabolic pathways of carotenoids such as p-carotene. CM = chylomicrons. VLDL = very low-density lipoproteins. LDL = low-density lipoproteins. HDL = high-density lipoproteins. BCO = p-carotene 15,15 -oxygenase. BCO2 = p-carotene 9, 10 -oxygenase. LPL = lipoprotein lipase. RBP = retinol binding protein. SR-BI = scavenger receptor class B, type I. 

Navab, M., Imes, S.S., Hama, S.Y., Hough, G.P., Ross, L.A., Bork, R.W., Valente, A.J., Berliner, J.A., Drinkwater, D.C., Laks, H. and Fogelman, A.M. (1991). Monocyte transmigration induced by modification of low density lipoprotein in cocultures of human aortic endothelial cells is due to induction of monocyte chemotactic protein 1 synthesis and is abolished by high density lipoprotein. J. Clin. Invest. 88, 2039-2046. 

Lipoproteins. A lipoprotein is an endogenous macromolecule consisting of an inner apolar core of cholesteryl esters and triglycerides surrounded by a monolayer of phospholipid embedded with cholesterol and apoproteins. The functions of lipoproteins are to transport lipids and to mediate lipid metabolism. There are four main types of lipoproteins (classified based on their flotation rates in salt solutions) chylomicrons, very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). These differ in size, molecular weight, and density and have different lipid, protein, and apoprotein compositions (Table 11). The apoproteins are important determinants in the metabolism of lipoproteins—they serve as ligands for lipoprotein receptors and as mediators in lipoproteins interconversion by enzymes. 

Blatter, M.-C., James, R.W., Messner, S., Barja, F., Pometta, D. (1993). Identification of a distinct human high-density lipoprotein subspecies defined by a lipoprotein-associated protein, K-45. Identity of K-45 with paraoxonase. Eur. J. Biochem. 211, 871. 

The recent years have seen the success of statins like Lipitor (atorvastatin) as hypolipidemic agents that help treating cardiovascular disease primarily by lowering low-density lipoproteins ( bad cholesterol ) levels. Another novel strategy is to tackle the same problem by elevating high-density lipoproteins (H D L or good cholesterol ) levels via inhibition of cholesteryl ester transfer protein (CETP). 

Soine PJ, Blanke RV, Guzelian PS, et al. 1982. Preferential binding of chlordecone to the protein and high density lipoprotein fractions of plasma from humans and other species. J Toxicol Environ Health 9 107-118. 

Many of the globulins act as transport proteins. Of particular interest are those proteins which are combined with lipids, themselves synthesized in the liver, to form lipoprotein complexes. High density lipoprotein (HDL), which contains predominantly apoproteins A and C combined with mainly phospholipids (most of the cholesterol found in mature HDL is added later) and very low density lipoprotein... 

HDL (high-density lipoprotein) a protein-lipid complex that carries cholesterol away from the tissues good cholesterol. ... 

Lipoproteins are an important class of serum proteins in which a spherical hydrophobic core of triglycerides or cholesterol esters is surrounded by an amphipathic monolayer of phospholipids, cholesterol and apolipoproteins (fatbinding proteins). Lipoproteins transport lipid in the circulation and vary in size and density, depending on their proteindipid ratio (Figure 7.3). Lipoprotein metabolism is adversely affected by obesity low-density lipoprotein (LDL)-cholesterol and plasma triglyceride are increased, together with decreased high-density lipoprotein (HDL)-cholesterol concentrations. 

Lipoproteins are classified into five groups. In order of decreasing size and increasing density, these are chylomicrons, VLDLs (very-low-density lipoproteins), IDLs (inter-mediate-density lipoproteins), LDLs (low-density lipoproteins), and HDLs (high-density lipoproteins). The proportions of apoproteins range from 1 % in chylomicrons to over 50% in HDLs. These proteins serve less for solubility purposes, but rather function as recognition molecules for the membrane receptors and enzymes that are involved in lipid exchange. 

Fic. 3. Protein components of human serum very high-density lipoprotein (VLDL) apoprotein (Apo). According to the experience gained in this laboratory, this component is negligible. As shown by Brown et al. (B9, BIO), it becomes relevant in VLDL of patients with types IV and V hyperlipoproteinemia,... 

El. Edelstein, C., Lim, C. T., and Scanu, A. M., On the subunit structure of the protein of human serum high density lipoprotein. I. A study of its major polypeptide component (Sephadex, fraction III). J. Biol. Chem. 247, 5842-5849 (1972). 

Shore, B., and Shore, V., Heterogeneity in protein subunits of human serum high density lipoproteins. Biochemistry 7, 2773-2777 (1968). 

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