Plasma glycoproteins

The von Willebrand factor (vWf) is a heterogeneous multimeric plasma glycoprotein produced by megakaryocytes and endothelial cells which is found in platelets, plasma and the subendothelium. Subendothelial vWf facilitates platelet adhesion, especially under high shear stress, by binding to glycoprotein GPIb-V-IX, a complex of four leucine-rich repeat proteins on platelets. 

Fibrinogen (factor I, 340 kDa see Figures 51-1 and 51-4 and Tables 51-1 and 51-2) is a soluble plasma glycoprotein that consists of three nonidentical pairs of polypeptide chains (Aa,Bpy)2 covalently linked by disulfide bonds. The B(3 and y chains contain asparagine-linked complex oligosaccharides. All three... 

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.

Additional protein constituents of the intrinsic cascade include prekallikrein, an 88 kDa protein zymogen of the protease kallikrein, and high molecular mass kininogen, a 150 kDa plasma glycoprotein that serves as an accessory factor. 

Renin [2] is an aspartate proteinase (see p. 176). It is formed by the kidneys as a precursor (prorenin), which is proteolytically activated into renin and released into the blood. In the blood plasma, renin acts on angiotensinogen, a plasma glycoprotein in... 

The protein of transfer of cholesteryl esters (CEPT) is a plasma glycoprotein that plays an important role in the control of the circulating rates of high and low density cholesterol (HOC and LDC, respectively). This is now a therapeutic target in the... 

Plasma proteins have been shown to be incorporated into normal bone matrix230,231,238. One plasma glycoprotein, identified in the human as the a2-HS-glycoprotein, is concentrated in bone and permanent dentine between 30—100 times in comparison with other plasma proteins. The a2-HS-glycoprotein is also concentrated in comparison with serum albumin in the mineral phase following either the... 

Once absorbed, vitamin B12 is transported to the various cells of the body bound to a plasma glycoprotein, transcobalamin II. Excess vitamin Bi2 is transported to the liver for storage. Significant amounts of vitamin B,2 are excreted in the urine only when very large amounts are given parenterally, overcoming the binding capacities of the transcobalamins (50-100 Mg). 

The molecular mechanism whereby cells recognize, interact with, and internalize glycoprotein molecules is discussed in two papers. Distler and colleagues describe the much studied but controversial role of glycosidically bound D-mannose-6-phosphate in the cellular assimilation of the enzyme /J-D-galactosidase Ashwell and Morgan study the metabolic fate of plasma glycoproteins in fish. 

An absence of R-type binding protein has been reported in two adult siblings by Carmel and Herbert (C20). R-Type protein was virtually absent from their leukocytes and saliva, and as was expected they had very low levels of serum vitamin B12. The absence of the protein did not appear to have any adverse effects. Other members of this family have also been found to have an absence of, or very low levels of, R-protein (H26). There was no general deficiency of plasma glycoproteins in these patients and the amounts of thyroid binding globulin, thyroxine, ceruloplasmin, and transferrin were all normal. 

CETP is a hydrophobic plasma glycoprotein, mainly synthesized in the liver, that possesses the unique ability to facilitate the transfer of cholesteryl ester (CE). CETP circulates in the blood, bound predominantly to HDL. CETP mediates the transfer of cholesteryl esters from HDL to VLDL and LDL in exchange for triglycerides. CETP also promotes the transformation of HDL2 to HDL3, an action that could promote reverse cholesterol transport. CETP inhibition produces an increase in HDL by markedly delaying the catabolism of apoA-I and A-II (129), an action that increases reverse cholesterol transport. These actions of CETP suggest that CETP inhibition could prevent atherosclerosis (130-132). 

Raynes, J. G. (1982) Variauons in the relative proportions of microheterogeneous forms of plasma glycoproteins in pregnancy and disease. Btomedtctne 36, 77-86. 

Additional proteins derived from Vg, the yolk plasma glycoproteins (YGPs), were recently discovered in the chicken214. Based on recent molecular biological analyses,... 

Yamamura, J.I., T. Adachi, N. Aoki, H. Nakajima, R. Nakamura and T. Matsuda. Precursor-product relationship between chicken vitellogenin and the yolk proteins the 40 kDa yolk plasma glycoprotein is derived from the C-terminal cysteine-rich domain of vitellogenin II. Biochim. Biophys. Acta 1244 384-394, 1995. 

Sammy, T. S. A., Chemical modification of sheep plasma glycoprotein. Arch. Biochem. Biophys. 121, 703-710 (1967). 

Corticosteroid-Binding Globulin (CBG) is a plasma glycoprotein that binds glucocorticoids with high affinity it is responsible for transport and bioavailability of these hormones. 

White, H., Totty, N., Panayotou, G. (1993). Haemonectin, a granulocytic-cell-binding protein, is related to the plasma glycoprotein fetuin. Eur. J. Biochem. 213, 523-528. 

AFM images of the von Willebrand factor, which is a plasma glycoprotein, in hemostasis and thrombosis of blood were reported. The size of the glycoprotein as measured by AFM was some two to three times larger than that reported by electron microscopy. Other authors have also reported similar divergences for other systems, which may be ascribed to such factors as ambient huntidity. 

Rat plasma glycoproteins, but not human, contain terminal G-acetyl, V-glycolyl-neuraminic acids in the carbohydrate side-chains of acute-phase glycoproteins (predominantly AGP) [10]. 

E. coli Calves Gastrointestinal tract Glycopeptides of bovine plasma glycoproteins [158]... 

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