Purification and composition of colonic epithelial mucin.

Colonic mucin was purified from homogenized scrapings of rat colonic epithelial cells using gel filtration and ion-exchange chromatography. High molecular weight water-soluble mucin was separated from low molecular weight proteins by gel exclusion chromatography on Sepharose 4B, and was further separated into two major mucin fractions and several non-mucin fractions on DEAE-cellulose. Fraction IV, the major mucin, was a sulphated glycoprotein with 62% carbohydrate by weight, and high concentrations of serine and threonine. A more acidic mucin, fraction V, had similar composition. Approx. 85% of the sialic acid of fractions IV and V were removed after incubation with Clostridium perfringens neuraminidase. Blood group A but not group H activity was present in fractions III, IV, and V. Ultracentrifugation experiments showed that fraction IV migrated as a single peak, whereas fraction V contained two components. Our study indicates that colonic mucin consists of at least two closely related acidic high molecular weight glycoproteins which can be separated from non-mucin contaminants by ion-exchange chromatography.