Glycoproteins incorporation into

BVdU is incorporated into DNA, but since it is phosphorylated specifically in the viraHy infected cell, incorporation is mainly confined to such cells. Evidence suggests that BVdU also inhibits the biosynthesis of HSV-1 glycoproteins, which may contribute to the inhibition of the HSV-1 vims (32). 

Evidence for Intracellular Feruloylation Reactions. The reactions by which feruloyl residues are added to polysaccharides occur intracellularly. This was established for the Fer-Ara2 units of the pectic polysaccharides of culture spinach cells by administration of [3H]arabinose so that the careers of polymer-bound pentose residues could be followed from their intracellular incorporation into nascent polysaccharides and glycoproteins, via their secretion through the plasma membrane, to their ultimate fate within the wall (28). The cells were fed [3H]arabinose for various defined periods of time, after which two distinct analyses were performed (Fig. 3) ... 

Various studies have shown the toxicity of various free monosaccharides towards mammalian cells. L-Fucose was found to inhibit the growth of some cells in culture, but only at high doses,292 and to inhibit the growth of implanted, mammary tumors in rats.293 In an examination of the effect of 93 carbohydrates on cell proliferation,294 D-fucose was one of the 42 that were toxic or growth-inhibitory, but the effect of L-fucose was not reported. The inhibitory effect of L-fucose in implanted, mammary tumors293 was considered to be accompanied by its incorporation into serum glycoproteins, and this would offer a possible explanation for some of its biological properties. 

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... 

Triffitt, J. T., Owen, M. Studies of bone matrix glycoproteins. Incorporation of 1 -14C glucosamine and plasma [14C] glycoprotein into rabbit cortical bone. Biochem. J. 136,125 (1973)... 

The involvement of glycolipid and glycoprotein intermediates in the synthesis of polysaccharides from glycosyl-nucleotides in plants is considered to be a likely possibility. Such intermediates could act as specific primers, or acceptor substrates, for the formation of polysaccharides. Furthermore, subunits of complex heteropolysaccharides could be assembled on such intermediates, and later incorporated into polysaccharides, or directly cross-linked into the cell wall. Evidence of the involvement of such intermediates in the synthesis of polysaccharides in a number of organisms is presented in Sections XII,3,b and XII,3,c. 

Transport of glycoproteins through the Golgi apparatus and their subsequent release or incorporation into a lysosome or the cell membrane. 

A protein of Mr 55,000 in guinea pig milk lipid globule membranes appears to be similar but not identical to the bovine proteins using peptide mapping techniques and solubility in aqueous solutions as comparative criteria (Johnson et al. 1985). This protein is synthesized in a membrane-bound form and becomes progressively solubilized after incorporation into intracellular membranes (Mather et al 1984), a property shared by several other peripheral membrane proteins, e.g., the glycoprotein GP2 in the pancreas (Scheffer et aL 1980). 

The increase in incorporation into polypeptides of lower molecular weights may be due to their faster diffusion rate in membrane, thus allowing them to undergo faster sialylation than the higher molecular weight species. This proposition is based on the assumption that there is only one species of glycoprotein sialyl-transferase, an assumption, which is evident later, may not be true. 

LDLs are then taken up by target cells through receptor-mediated endocytosis (see Topic E4). The LDL receptor, a transmembrane glycoprotein on the surface of the target cells, specifically binds apoB-100 in the LDL coat. The receptors then cluster into clathrin-coated pits and are internalized (see Topic E4, Fig. 3). Once in the lysosomes, the LDLs are digested by lysosomal enzymes, with the cholesterol esters being hydrolyzed by a lysosomal lipase to release the cholesterol (Fig. 1). This is then incorporated into the cell membrane and any excess is re-esterified for storage by acyl CoA cholesterol acyltransferase (ACAT). 

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