Subunit interactions and physical properties of bovine gallbladder mucin

In this study the interaction of gallbladder mucin subunits was examined by gel permeation chromatography, quasielastic laser light scattering, and viscometry. Purified mucin eluted primarily in the void volume of a Sepharose 2B-Cl column, indicating a molecular weight above 2 x 10(6). Disaggregation of the mucin polymer resulted in the elution of glycoprotein in the included volume of the Sepharose 2B-Cl column. Gallbladder mucin had a hydrodynamic radius of 630 A that was independent of mucin concentration below 2 mg/ml. At mucin concentrations above 2 mg/ml, a concentration-dependent increase in both hydrodynamic radius and apparent viscosity of gallbladder mucin was observed. Mucin demonstrated a strong pH dependence in hydrodynamic radius and viscosity with the maximum occurring at approximately pH 5.5. These findings suggest that noncovalent interactions participate in bovine gallbladder mucin subunit associations. Furthermore, changes that occur in the physicochemical environment of the gallbladder during periods of stasis may enhance the viscoelastic properties of mucin and promote the accumulation of biliary sludge in the gallbladder.