Carbohydrates derived from glycoproteins

Of particular importance are carbohydrates that are connected to proteins. They are called glycoproteins. Until the 1960s, protein chemists did not give much credit to carbohydrates. Today, we know that most of the eukaryotic proteins exist in a glycosylated form and that 90% of their total molecular weight is attributed to the carbohydrate moiety. Glycoproteins are found in all biological areas 

The most important function of carbohydrates is their role as a mediator in cellular communication [190]. They participate in processes such as insemination, differentiation and aggregation of organs as well as in bacterial and viral cell infection [191]. It is obvious that new therapeutic possibilities are opening up in the fight against disease. Free ohgosaccharides found in human milk are 

The structural diversity becomes even more complex by  

---

Due to the high number and complexity of potential carbohydrate compounds, a number of methods have been developed that allow identification of carbohydrate structures, depending on the analytical problem and conditions, either directly or in combination with other techniques. In general, oligosaccharide analysis derived from glycoproteins is divided into three phases ... 

Figure 10.344 Experimental strategy for analyzing carbohydrates derived from membrane-coupled glycoproteins.

Multiple-ion monitoring is, however, of considerable value in structural studies, but only if model compounds of known structure are available for comparison. Such an approach has been used in the study of the carbohydrate structures of glycoproteins from different tissues.50 Separation of glycopeptides obtained from various tissues was performed on columns of concanavalin A-Sepharose. Structural analysis by multiple-ion monitoring of partially methylated, alditol acetates derived from the various fractions indicated that the glycopeptides were separated according to the linkage pattern of mannose (see Fig. 1). 

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. 

---