Conjugated proteins containing a complex carbohydrate moiety linked to the protein chain are referred to as glyco- and mucoproteins. A large number are known with considerable individual variation in composition and properties. The carbohydrate chain linked to the protein is made up of the hexoses, galactose; the methylpentose, fucose; and a sialic acid, such as N-acetylneuraminic acid. The sialic acid is located at one end of the carbohydrate chain; the other end of the chain is linked by a peptide bond to one of the peptide chains of the protein molecule.
In a useful classification, those carbohydrate-proteins containing less than 4 per cent of hexosamines are termed glycoproteins. They contain from a trace up to about 15 per cent of total carbohydrate. Those with over 4 per cent of hexosamines and containing from 10 to 75 per cent of carbohydrate are termed mucoproteins. The expression mucoids is also used in characterizing those mucoproteins in which the bond linking the carbohydrate chain and the protein is split only with difficulty, in contrast to another group containing acidic mucopolysaccharides, in which the linkage is polar and easily split. The glyco- and mucoproteins differ from the albumins and globulins in that they are not precipitated by perchloric and sulfosalicylic acids.
Mucoproteins of clinical interest are found in both serum and urine. Electrophoretically, most mucoproteins migrate with a mobility associated with alpha-1 globulins, although individual proteins may be found among all the usual electrophoretic groups. They are identified on electrophoretic strips or gels by their capacity to give a positive staining reaction with Schiff's reagent. The characteristic pink color is due to a reaction between the carbohydrate portion of the mucoprotein and the reagent. The mucoid present in serum in greatest amount is orosomucoid; it has a molecular weight of about 40,000 and is quite acidic, possessing an isoelectric point at pH 2.3. A number of other mucoproteins are also present in varying amounts.
Mucoproteins of clinical interest are found in both serum and urine. Electrophoretically, most mucoproteins migrate with a mobility associated with alpha-1 globulins, although individual proteins may be found among all the usual electrophoretic groups. They are identified on electrophoretic strips or gels by their capacity to give a positive staining reaction with Schiff's reagent. The characteristic pink color is due to a reaction between the carbohydrate portion of the mucoprotein and the reagent. The mucoid present in serum in greatest amount is orosomucoid; it has a molecular weight of about 40,000 and is quite acidic, possessing an isoelectric point at pH 2.3. A number of other mucoproteins are also present in varying amounts.
Myelin Oligodendrocyte Glycoprotein (MOG) is a glycoprotein believed to be important in the process of myelinization of nerves in the central nervous system (CNS). MOG (35-55)
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