The isolation, purification, tissue localization and identification of a glycoprotein found in the crude mucus gel of patients with carcinoma of the stomach

Doctoral Thesis


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University of Cape Town

The thin layer of crude mucus lining the human gastric mucosa protects the delicate gastric epithelium from the high shear forces associated with digestion. Gastric mucus is composed largely of water (>90%) and a complex mixture of organic components such as enzymes, various serum and cellular macromolecules, sloughed cells, bactericidal proteins, plasma proteins, inorganic ions and very importantly the mucins, that impart to it its gel-forming properties. Mucins are large heterogenous polymers that are difficult to characterize by traditional biochemical methods. However mucins from different regions of the body do share common features such as a low protein content of approximately 20% by weight and a carbohydrate content of 70 to 80% by weight. Mucins are characterized by a variable number of tandem repeat regions rich in serine, threonine and proline with the serine and threonine being potential sites for O-glycosylation. In contrast to the glycosylated region is the 'naked' region rich in cysteine and susceptible to proteolysis. The cysteine residues enable mucin monomers to form polymers by disulphide bridges. Alterations of mucin expression take place in gastric carcinomas. Our laboratory previously reported the presence of a 40-50 kDa glycoprotein in the mucus of patients with gastric cancer that associated with albumin. The primary aims of our study were to develop an antibody to this 40-50 kDa glycoprotein, and to determine the location of its expression in gastric tissue by the immunohistochemical method, ranging from normal, to premalignant to cancer. The final aim was to identify this unknown glycoprotein by proteomic analysis. The reactivity of the antibody to the mucin and its 40-50 kDa component was determined by Western Blotting.

Includes bibliographical references (leaves 101-138).