POLYELECTROLYTE BEHAVIOUR IN MUCUS GLYCOPROTEINS STEPHEN E. HARDING " and J. MICHAEL CREETH' " Departmenr of Biochemistry, (lnioersity of Bristo!, Bristot BS8 ITD and h lJnioersity of Bristol Department of Medicine, Bristol Royal Infirmary, Bristol BS2 8HW (U.K.) (Received February 7th. 1983) Key words: Glycoprotein; Polyelectrolyte effect; Viscosity; Conformational change; (Human ooarian cyst and sputum) Mucus glycoproteins isolated from a human ovarian cyst and the sputum of a cystic fibrotic exhibit a significant decrease in reduced viscosify with increase in ionic strength, I. The molecular weights of the glycoproteins showed little variation with 1, implying that the change is conformational rather than a dissociation. This change is ascribed to a polyelectrolyte-type contraction rather than to a reduction in particle asymmetry. Guanidine hydrochloride acts as a classical electrolyte in the reversible suppression of charge effects, and not as a denaturing or dissociation agent. These observations help to resolve some discrepanciesin earlier studies. The occurrence of polyelectrolyte effects in these glycoproteins is ascribed to flexibility of structure and to their content of N-acetylnerrraminic acid. The ionic strength values necessary for different types of physical measurement are discussed. il4 BBA 31654 Introduction Although high concentrations of electrolytesor protein denaturants have often been employed to solubilize gelatinousmucous secretions (see, e.g., refs. I -4), conflicting claims have been made [4,5-8] as to whether these substances have a deleterious effect on the glycoprotein components of the secretions. The main interest lies in the occurrence of any conformational change, or dis- sociation, and the extent of reversibility of such phenomena, if found. Therefore, we have studied the effect of guanidinium hydrochloride up to 6 M, and sodium chloride up to I M, on three representativeglycoproteins. The techniques cho- sen were viscometry and molecular weight mea- surement, these being the most informative in respect of the changes anticipated. Because the apparent molecular weights of macro-ionic species at very low ionic strengths are difficult to interpret [9], we have restricted the observations to ionic strengths greater than 0. l0 M. The results are 0167-4838/83/$03.00 o 1983 Elsevier Science Publishers B.V. Biochimica et Biophysica Acta, 746 (1983) I l4-l l9 Elsevier useful in showingthe minimum salt concentrations necessary for various types of physico-chemical measurement. Materials and Methods Soloents.The primary solvent used throughout was a phosphate/chloride buffer, pH 6.8, 1 0.10, of the following composition: 0.033 M NaCl, 0.0167 M NarHPOo, 0.0167M NaHrPO., 0.002 M NaNr, 0.001 M EDTA. GUHCI and NaCl solutions were prepared in this solvent. For the density-gradient experiments, CsrSOo to a weight fraction of 0.3l5 was added. Glycoproteinr. Two of the glycoproteins were prepared from human ovarian cysts by the phenol-extraction, ethanol fractionation, method of Morgan [0]. One of these (603 AmS) was soluble in hot saturated ammonium sulphate, was the most carbohydrate-rich and had the lowest molecular weight of the six main fractions isolated from this cyst Il]. The other cyst glycoprotein