Glycoprotein bodies

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.)... 

These proteins are called acute phase proteins (or reactants) and include C-reactive protein (CRP, so-named because it reacts with the C polysaccharide of pneumococci), ai-antitrypsin, haptoglobin, aj-acid glycoprotein, and fibrinogen. The elevations of the levels of these proteins vary from as little as 50% to as much as 1000-fold in the case of CRP. Their levels are also usually elevated during chronic inflammatory states and in patients with cancer. These proteins are believed to play a role in the body s response to inflammation. For example, C-reactive protein can stimulate the classic complement pathway, and ai-antitrypsin can neutralize certain proteases released during the acute inflammatory state. CRP is used as a marker of tissue injury, infection, and inflammation, and there is considerable interest in its use as a predictor of certain types of cardiovascular conditions secondary to atherosclerosis. Interleukin-1 (IL-1), a polypeptide released from mononuclear phagocytic cells, is the principal—but not the sole—stimulator of the synthesis of the majority of acute phase reactants by hepatocytes. Additional molecules such as IL-6 are involved, and they as well as IL-1 appear to work at the level of gene transcription. 

Transferrin (Tf) is a Pj-globulin with a molecular mass of approximately 76 kDa. it is a glycoprotein and is synthesized in the liver. About 20 polymorphic forms of transferrin have been found, it plays a central role in the body s metabolism of iron because it transports iron (2 mol of Fe + per mole of Tf) in the circulation to sites where iron is required, eg, from the gut to the bone marrow and other organs. Approximately 200 billion red blood cells (about 20 mL) are catabolized per day, releasing about 25 mg of iron into the body—most of which will be transported by transferrin. 

While direct infection of the nenrons by HIV is not likely to be an important mechanism of nenrotoxicity (Pardo et al. 2001), there is a complex interplay of HIV envelope glycoprotein gpl20 nenrotoxicity and other immunopathogenic factors in the mechanisms of axonal or nenronal injury (Hoke and Comblath 2004). HIV infection most likely canses DRG cell body and axonal damage via different mechanisms of injnry in each structure (Hahn et al. 2008). 

FIG. 2 Mechanisms of drug transfer in the cellular layers that line different compartments in the body. These mechanisms regulate drug absorption, distribution, and elimination. The figure illustrates these mechanisms in the intestinal wall. (1) Passive transcellular diffusion across the lipid bilayers, (2) paracellular passive diffusion, (3) efflux by P-glycoprotein, (4) metabolism during drug absorption, (5) active transport, and (6) transcytosis [251]. 

This process seems to reflect gradual increases in the intensity and density of labelled receptor cell bodies and their axons, followed by regional bulbar staining as synaptogenesis proceeds. However, a more extensive range of lectins needs to be examined before the implications of species differences in the membrane glycoproteins can be satisfactorily interpreted (Salazar and Quinteiro, 1998). 

Figure 4.4 Comparison of oxidase-dependent iron transport in mammals and yeast. In mammals, the plasma glycoprotein cerulpolasmin mediates iron oxidation, facilitating iron export from the cells and delivery to other tissues throughout the body. In yeast, Fet3p, an integral membrane protein mediates iron oxidation, resulting in plasma membrane iron transport through the permease Ftrlp. Reprinted from Askwith and Kaplan, 1998. Copyright (1998), with permission from Elsevier Science.

Virtually all therapeutic glycoproteins, even when produced naturally in the body, exhibit such heterogeneity for example, two species of human interferon-y (IFN-y), one of molecular mass 20 kDa and the other of 25 kDa, differ from each other only in the degree and sites of (N-linked)... 

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