Isolation and partial characterization of a soluble mucin in human pancreatic juice

Morphological and histochemical abnormalities in pancreatic mucin occur in many pancreatic disorders. However, the composition of pancreatic mucin is poorly understood. Purified mucin was isolated from pure pancreatic juice by sequential chromatography on Sepharose CL-2B and CL-4B followed by CsCl density gradient ultracentrifugation. The mucin preparation consists of 24% protein and 73% carbohydrate. Reduction of the macromolecule (greater than 2 x 10(6)) by mercaptoethanol resulted in the formation of subunits of molecular weight 500,000 and released several small molecular weight proteins, including a glycoprotein of an average molecular weight of 116,000. Cellulose acetate electrophoresis separated the mucin into three species of different staining properties for periodic acid-Schiff reagent and Alcian blue, suggesting the presence of microheterogeneity with respect to sulphation and sialation. Threonine, serine, and proline composed 48% of the total amino acids, while the oligosaccharide moiety contained N-acetylglucosamine, N-acetylgalactosamine, fucose, galactose, sialic acid, and sulphate. We also detected the presence of C16:0 and C18:0 fatty acids which were probably noncovalently bound to the pancreatic mucin.