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Apoprotein synthesis

Inhibits VLDL synthesis and apoprotein synthesis in hepatocytes and T HDL —>4- plasma VLDL, LDL, and TGs. Activates lipoprotein lipases. [Pg.127]

LDL (apo B-lOO, E) receptors occur on the cell surface in pits that are coated on the cytosolic side of the cell membrane with a protein called clathrin. The glycoprotein receptor spans the membrane, the B-lOO binding region being at the exposed amino terminal end. After binding, LDL is taken up intact by endocytosis. The apoprotein and cholesteryl ester are then hydrolyzed in the lysosomes, and cholesterol is translocated into the cell. The receptors are recycled to the cell surface. This influx of cholesterol inhibits in a coordinated manner HMG-CoA synthase, HMG-CoA reductase, and, therefore, cholesterol synthesis stimulates ACAT activ-... [Pg.223]

As an example, the low-density lipoprotein (LDL) molecule and its receptor (Chapter 25) are internalized by means of coated pits containing the LDL receptor. These endocytotic vesicles containing LDL and its receptor fuse to lysosomes in the cell. The receptor is released and recycled back to the cell surface membrane, but the apoprotein of LDL is degraded and the choles-teryl esters metabolized. Synthesis of the LDL receptor is regulated by secondary or tertiary consequences of pinocytosis, eg, by metabolic products—such as choles-... [Pg.430]

The liver plays a decisive role in the cholesterol metabolism. The liver accounts for 90% of the overall endogenic cholesterol and its esters the liver is also impli-cated in the biliary secretion of cholesterol and in the distribution of cholesterol among other organs, since the liver is responsible for the synthesis of apoproteins for pre-p-lipoproteins, a-lipoproteins, and P-lipoproteins which transport the secreted cholesterol in the blood. In part, cholesterol is decomposed by intestinal micro-flora however, its major part is reduced to coprostanol and cholestanol which, together with a small amount of nonconverted cholesterol, are excreted in the feces. [Pg.209]

In adult brain most cholesterol synthesis occurs in astrocytes. Apoprotein E (apoE) is the major apolipopro-tein of the CNS and it is secreted by astrocytes. In astrocyte cultures apoE appears in the media as cholesterol-rich particles of a size similar to peripheral HDL (5-12 nm) (Fig. 2-7). The ATP-dependent transporter ABCA1, expressed by both astrocytes and neurons, promotes the formation of the apoE-stabilized high-density lipoprotein (HDL)-sized particles from astrocytic cholesterol. [Pg.26]

Mitochondrial DNA is inherited maternally. What makes mitochondrial diseases particularly interesting from a genetic point of view is that the mitochondrion has its own DNA (mtDNA) and its own transcription and translation processes. The mtDNA encodes only 13 polypeptides nuclear DNA (nDNA) controls the synthesis of 90-95% of all mitochondrial proteins. All known mito-chondrially encoded polypeptides are located in the inner mitochondrial membrane as subunits of the respiratory chain complexes (Fig. 42-3), including seven subunits of complex I the apoprotein of cytochrome b the three larger subunits of cytochrome c oxidase, also termed complex IV and two subunits of ATPase, also termed complex V. [Pg.706]

Although both LDL and HDL are primarily cholesterol particles, most of the cholesterol measured in the blood is assodated with LDL. The normal role of LDL is to deliver cholesterol to tissues for biosynthesis. When a cell is repairing membrane or dividing, the cholesterol is required for membrane synthesis. Bile acids and salts are made from cholesterol in the liver, and many other tissues require some cholesterol for steroid synthesis. As shown in Figure 1-15-6, about 80% of LDL are picked up by hepatocytes, the remainder by peripheral tissues. ApoB-100 is the only apoprotein on LDL, and endocytosis of LDL is mediated by apoB-100 receptors (LDL receptors) clustered in areas of cell membranes lined with the protdn clathrin. [Pg.214]

Thioneins are apoproteins that are exceptionally sulfur-rich (composed of greater 30 mol% cysteine). These proteins are found in high abundance in liver and kidney cytoplasm where they form metallothioneins (the holo-protein forms) upon complexation with metal ions. Thi-onein synthesis is induced by the presence of metals, especially zinc, copper, mercury, and cadmium. [Pg.457]

The answer is D. This patient s tests indicate that he has severe hypercholesterolemia and high blood pressure in conjunction with atherosclerosis. The deaths of several of his family members due to heart disease before age 60 suggest a genetic component, ie, familial hypercholesterolemia. This disease results from mutations that reduce production or interfere with functions of the LDL receptor, which is responsible for uptake of LDL-cholesterol by liver cells. The LDL receptor binds and internalizes LDL-choles-terol, delivers it to early endosomes and then recycles back to the plasma membrane to pick up more ligand. Reduced synthesis of apoproteins needed for LDL assembly would tend to decrease LDL levels in the bloodstream, as would impairment of HMG CoA reductase levels, the rate-limiting step of cholesterol biosynthesis. Reduced uptake of bile salts will also decrease cholesterol levels in the blood. [Pg.121]

Molecular basis of carbon tetrachlori de-i nduced steatosis effect of carbon tetrachloride on synthesis of apoproteins. [Pg.104]

The elevation of HDL levels by fibrates may be due to two drug actions induced synthesis of apo-Al, the principal apoprotein of HDL, and increased assembly of new HDL particles in the circulation. Sirrface components of VLDL contribute to formation of HDL, as the VLDL particles are reduced in size through the action of LPL. The increased rate of catabolism of VLDL caused by the fibrates would provide more components for assembly of HDL particles. [Pg.274]

As well as induction of the synthesis of the apoprotein portion of cytochrome P-450, there is also induction of the synthesis of the heme portion. Clearly, it is also necessary to have an increased amount of heme if there is an increase in the amount of the enzyme apoprotein being synthesized. Thus, the rate-limiting step in heme synthesis, the enzyme 5-aminolaevulinate synthetase, is inducible by both phenobarbital and TCDD. This is the result of transcriptional activation of the gene, which codes for the S-aminolaevulinate synthetase. It may be that the decrease in the heme pool, which results from incorporation of heme into the newly synthesized apoprotein, leads to derepression of the gene and hence increased mRNA synthesis. The gene repression could be heme-mediated, or heme may modulate P-450 genes. [Pg.178]

The synthesis of the apoproteins takes place on ribosomes that are bound to the endoplasmic reticulum. As we mentioned previously, the biosynthesis of the other lipids in lipoproteins (cholesterol, triacylglycerols, and phospholipids) also occurs on the endoplasmic reticulum. [Pg.469]

Postulated scheme for the synthesis, assembly, and secretion of VLDL by a hepatocyte (liver cell). (1) Synthesis The apoproteins, phospholipid, triacylglycerol, cholesterol, and cholesteryl esters are synthesized in the endoplasmic reticulum. (2) Assembly These components are assembled into a prelipoprotein particle in the lumen of the endoplasmic reticulum. (3) Processing The particle moves to the Golgi apparatus, where modification of the apoproteins occurs. [Pg.470]

O Brian, M.R., Kirshbom, P.M. Majer, R.J. (1987). Bacterial heme synthesis is required for expression of the leghemoglobin but not the apoprotein in soybean nodules. Proceedings of the National Academy of Sciences (USA) 84, 8390-3. [Pg.200]

Increased levels of apolipoproteins and rate-limiting enzymes of lipogenesis and their mRNAs have been demonstrated in the liver of nephrotic rats (V5), although increased liver cholesterol synthesis has not been confirmed in nephrotic patients (D9). Cholesterol synthesis in the liver probably does not change during antipro-teinuric treatment (D9). The rate of synthesis of LDL apoprotein B is variable and depends on the presence or absence of hypertriglyceridemia (V6). [Pg.198]

VLDLs are synthesized in the liver and transport triacylglycerols, cholesterol and phospholipids to other tissues, where lipoprotein lipase hydrolyzes the triacylglycerols and releases the fatty acids for uptake. The VLDL remnants are transformed first to IDLs and then to LDLs as all of their apoproteins other than apoB-100 are removed and their cholesterol esterified. The LDLs bind to the LDL receptor protein on the surface of target cells and are internalized by receptor-mediated endocytosis. The cholesterol, which is released from the lipoproteins by the action of lysosomal lipases, is either incorporated into the cell membrane or re-esterified for storage. High levels of intracellular cholesterol decrease the synthesis of the LDL receptor, reducing the rate of uptake of cholesterol, and inhibit HMG CoA reductase, preventing the cellular synthesis of cholesterol. [Pg.339]

Three cytosolic factors were recently characterized that contribute specifically to the maturation of cytosolic and nuclear FeS proteins. Cfdl (Roy et al. 2003) and Nbp35 (Hausmann et al. 2005) are essential soluble P-loop ATPases. Except for a short N-terminal extension in Nbp35 that itself carries an FeS cluster, these two proteins are structurally very similar. Together with the third component, yeast Narl (or human Narf, nuclear prelamin A recognition factor), these proteins have dual nuclear and cytosolic localization. It is not clear what the molecular role these cytosolic factors play in the maturation of FeS proteins is. An attractive hypothesis is that the FeS clusters or their precursors are transferred into the target apoproteins with the assistance of cytosolic factors after their export from mitochondria. Alternatively, the cytosolic proteins may facilitate de novo synthesis of FeS clusters in the cytosol using some compounds which are produced by mitochondrial FeS proteins (Lill and Miihlenhoff 2005). [Pg.118]

Chylomicrons are triglyceride rich and contain apolipoprotein B-48 and the A types. The latter are synthesized in the intestinal tract cells. Additional apoproteins are transferred to the chylomicrons from HDL in circulation the apoE and apoC types. Their site of synthesis is the liver. The chylomicrons are subject to degradation by lipoprotein lipase in the peripheral tissue, especially adipose tissue. Lipoprotein lipase activity is increased by increased blood insulin levels. This enzyme is extracellular, attached to the capillary endothelial cells, and activated by ApoC-II, which is present in the chylomicrons. Lipoprotein lipase causes the hydrolysis of triglycerides, thus decreasing chylomicron size... [Pg.502]


See other pages where Apoprotein synthesis is mentioned: [Pg.290]    [Pg.580]    [Pg.499]    [Pg.499]    [Pg.3126]    [Pg.125]    [Pg.189]    [Pg.290]    [Pg.580]    [Pg.499]    [Pg.499]    [Pg.3126]    [Pg.125]    [Pg.189]    [Pg.62]    [Pg.223]    [Pg.241]    [Pg.34]    [Pg.302]    [Pg.141]    [Pg.120]    [Pg.18]    [Pg.132]    [Pg.218]    [Pg.239]    [Pg.225]    [Pg.388]    [Pg.534]    [Pg.88]    [Pg.276]    [Pg.119]    [Pg.124]    [Pg.250]    [Pg.391]    [Pg.529]    [Pg.529]    [Pg.678]   
See also in sourсe #XX -- [ Pg.469 ]




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