SOLVENT EFFECTS ON THE VISCOELASTIC BEHAVIOR OF PORCINE SUBMAXILLARY MUCIN

Rheological methods have been used to investigate the intermolecular i nteractions of porcine submaxillary mucins (PSM) in solution. PSM is a high molecular weight glycoprotein consisting of a linear, semi-flexi ble protein backbone to which a large number of oligosaccharides (1-5 saccharide units) are attached as side chains. Concentrated aqueous so lutions of PSM containing different amounts of guanidine hydrochloride (GdnHCl) were subjected to both controlled stress and controlled stra in theological analyses. In the absence of GdnHCl, PSM solutions exhib it viscoelastic properties characteristic of a gel: the storage modulu s, G', is much larger than the loss modulus, G'', at all deformation f requencies, and the compliance is 100% recoverable at small stresses, indicative of strong intermolecular interactions. In 3.0 M aqueous Gdn HC1, PSM forms a viscoelastic solution, with G'' > G' at all frequenci es and a relatively small recoverable compliance, pointing to disrupti on of the intermolecular interactions by the chaotropic salt. Intermed iate behavior is observed in 1.5 M GdnHC1, characteristic of a margina l gel: G' approximate to G'' and greater than 50% recoverable complian ce. In dilute solution, PSM behaves viscoelastically as a typical poly electrolyte. However, concentrated solutions are turbid, the turbidity decreasing as GdnHCl is added, indicating that extensive intermolecul ar association accompanies the gelation process. The results show that although PSM is secreted in nature as a viscous solution, it can form gels that are similar to those of tracheobronchial and gastric mucins , and suggest common features to the gelation mechanism, with the stre ngth of the gel correlated with the length of the oligosaccharide side chains.