Affiliations: [a] Department of Macromolecular Science, W.A. Bernbaum Cystic Fibrosis Research Center, Case Western Reserve University, Cleveland, Ohio, USA | [b] Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio, USA | [c] Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, USA
Note: [*] Present address: A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninski Pro 29, 117912 Moscow B-71, Russia.
Note: [**] Reprint requests to: A. M. Jamieson, Department of Macromolecular Science, Case Western Reserve University, 2100 Adelbert Road KHS 314, Cleveland, Ohio 44106-7202, USA; Fax: (216) 368-4202; E-mail: amj@po.cwru.edu.
Abstract: Rheological experiments have shown that canine submaxillary mucin (CSM) forms gels in aqueous solution at low ionic strength and in 6M GdnHCl. Examination of specimens of intact CSM and also its subunits prepared by reduction and carboxymethylation showed that the presence of lipid increases the gel-forming capability, probably as a result of enhancement of the intermolecular hydrophobic interactions. The rheological evidence for gelation is that substantially larger values of the oscillatory storage modulus, G’(ω), and the dynamic complex viscosity, η∗(ω), are observed for lipid-containing CSM. This is backed up by electron micrographs of freeze fractured specimens, where we observe a network morphology in which the cross-links are formed as a result of non-bonded interactions between a number of CSM chains. The intermolecular interactions responsible for gelation probably involve hydrophobic association between the interdigitated oligosaccharides, and/or between the non-glycosylated regions of the protein core, and can occur even in a highly chao tropic medium (6M GdnHCl). In contrast to previous experiments with porcine submaxillary mucin and human tracheobronchial mucin, which form microphase-separated gels in aqueous solution, CSM solutions undergo macroscopic phase separation into polymer-rich (gel) and polymer-poor (sol) phases. These data point to stronger hydrophobic interactions in lipid-containing CSM.
Keywords: Hydrophobic interactions, phase separation, gel formation
DOI: 10.3233/BIR-1997-344-504
Journal: Biorheology, vol. 34, no. 4-5, pp. 295-308, 1997
