Glycoprotein with hydrochloric acid

To establish the nature of the carbon-nitrogen bond of the carbohydrate-L-asparagine unit in glycoproteins, treatment of the synthetic derivatives 5 and 211 with hydrochloric acid was first studied in... 

The neuraminic acids (also called sialic acids), which occur in the terminal positions of carbohydrate moieties of many glycoproteins and ganglio-sides, must be hydrolyzed under very mild conditions. For example, hydrolysis with 0.01 M hydrochloric acid for 30 min at 100° causes 20% decomposition of N-acetylneuraminic acid. Sialic acids are more tolerant to methanolysis they may also be removed enzymically. 

Alpenfels and coworkers studied the hydrolysis of glycoproteins and keratin fibers with 1 or 2 M hydrochloric acid for various periods of time at 100°. These investigators found that the concentration of neutral monosaccharides from hard keratin reached a maximum after hydrolysis with 2 M hydrochloric acid for 2 h at 100°, and the yield of the neutral monosaccharides was linear up to 25 mg of hair per mL of hydrochloric acid solution. The latter fact shows that a relatively large amount of protein does not interfere with the analysis of a relatively small amount of carbohydrate. 

Neeser and Schweizer introduced 4 M CF3CO2H for 1 h at 121° for hydrolysis of glycoproteins. Both neutral and amino sugars were considered. They compared this method to hydrolysis with 0.6 M hydrochloric acid for 4 h at 100° and 3 M hydrochloric acid for 0.75 h at 125°. Hydrolysis of fetal-calf-serum fetuin, bovine submaxillary mucin, and horse-radish peroxidase showed hydrolysis with CF3CO2H to be superior. 

The use of ion-exchange resins for hydrolysis was introduced by Wadman,55 and this method is becoming increasingly popular in the field of glycoproteins. The resin may be used alone,56 in the presence of dilute sulfuric acid,57 or with dilute hydrochloric acid.58,59 The last... 

The Ehrlich reagent, developed originally for the colorimetric assay of pyrrole derivatives, was shown by Ehrlich to give a color with certain glycoproteins, with and without prior alkali treatment (3). The reagent consists of dimethylaminobenzaldehyde in strong hydrochloric acid. This assay later became the basis for the Morgan-Elson reaction for the deter-... 

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