Glycoproteins definition

Classification Glycoprotein Definition Taste-modifying protein from the African plant Richardella dulcifa Properties M.w.< 44,000 Uses Sweetener in foods Features Modifies sour taste to sweet taste... 

Coagulation factors are glycoproteins named by roman numbers (the numbers being ascribed at the time of the components definition, not sequence of activation) (Table 1). Besides von Willebrand factor (vWF), the coagulation factors are synthesized in the liver. They have very different half-lifes and different concentrations in the plasma. Several coagulation factors are stored in platelets and endothelial cells and can be released during activation of these cells, which can result in a much higher local concentration of the respective factor (e.g., vWF). 

In industrialised societies, most gallbladder stones are mixed in composition. They contain not only cholesterol but also bile pigments, calcium salts, mucus glycoprotein and often amorphous material. Nonetheless, they are still described as cholesterol-rich although the arbitrary definition for cholesterol-rich stones varies from author to author ranging from >70% to >90% by weight. 

Current available information does not permit definitive conclusions on the nature, specificity, and mechanism of action of the protein cofactor (s) of lipoprotein lipase. It is verj difiicult to correlate the observations described above (summarized in Table 10) since the enzyme preparations used were not pure or well characterized, and were derived from various sources. For instance, two species of lipoprotein lipase have been reported to exist in rat adipose tissue (G4), and major differences between enzymes of liver and adipose tissue have been noted (G16). Also, the nature of the apoprotein preparations employed as protein cofactor (s) of lipoprotein lipase has not been clearly specified in all the studies contaminated materials may account for the spurious results observed. At present, it is not known how apoproteins such as apo Glu, apo Ala, and apo Ser could exhibit their activator or inhibitor activity on lipoprotein lipase. If these different apoproteins indeed prove to be cofactors for lipoprotein lipase, the nature of the lipid-protein specificity must be established and thus the role played by carbohydrates, since some of these apoproteins are glycoproteins. 

By analogous considerations, glycoproteins may be described as macromolecules composed of one or more polypeptide chains that are formed by the normal processes of translation at the polysomal level and to which sugar molecules are attached through covalent bonds. There are a number of definitions of glycoproteins, and these have been fully discussed. The definition employed here is wider than those adopted by many workers in the past, as it has a number of advantages in the present discussion. 

Most of the lysosomal proteases called cathepsins are small 20- to 40-kDa glycoproteins found in all animal tissues.313 Most are cysteine proteases which function best and are most stable in the low pH reducing environment of lysosomes. They resemble papain in size, amino acid sequence, and active site structures. Papain is nonspecific but most cathepsins have definite substrate preferences. Cathepsin B is the most abundant. There are smaller amounts of related cathepsins H (an aminopeptidase)314 and L315 and still less of cathepsins C, K, and others. Cathepsin B is both an endopep-tidase and an exopeptidase.316 It acts on peptides with arginine at either Pj or P2 but also accepts bulky hydro-phobic residues in Pj and prefers tyrosine at P3.317 Cathepsin S is less stable at higher pH than other cathepsins and has a more limited tissue distribution, being especially active in the immune system.318 319... 

Various polymorphisms of the platelet surface proteins, such as glycoprotein (GP) la-lla, GPIb-V-IX, and GPIIb/llla have been reported. Afshar-Kharghan et al. (34) have recently reported a gene polymorphism in the Kozac sequence of the GpIba receptor. Definition of the role of these polymorphisms in arterial diseases is warranted. 

While the concept of purity is rather straightforward for small molecules, definition of purity for a protein product can be difficult. The difficulty in defining purity arises for several reasons 1) some products, glycoproteins in particular, exist in a... 

It is likely that the most definitive structural studies of biological polysaccharides will eventually come from those glycoproteins which can be obtained as single crystals suitable for X-ray structure analysis or from enzyme crystal structures where polysaccharides are the substrates. Even there, the results have hitherto been barely at the limits of atomic resolution, because of the overall size of the protein molecules. 

There is little work that definitively describes the composition of fungal adhesives. However, it is apparent that fungi do not share either common adhesives or mechanisms for adhesion. One factor that does appear with regularity is that the surface of fungal germ tubes are typically ensheathed by a glycoprotein/carbohydrate matrix (41, 51.r JU.) / and... 

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