The major nonreduced mucus glycoproteins (mucins) from sputa of cystic fibrosis (CF) and asthmatic patients have been purified to electrophoretic homogeneity and subjected to physical and chemical characterization. The sputum specimens were solubilized in buffer containing 0.22 M KSCN and fractionated on Bio-Gel A-5m, followed by digestion with DNase, rechromatography on the same column, and chromatography on hydroxylapatite. Sodium dodecyl sulfate gel electrophoresis of purified mucins gave a single band. Carbohydrate analyses of the purified mucins showed no significant differences in the sugar components from the two mucins. However, the CF mucin contained substantially higher (11%) sulfate content than that observed for the asthmatic mucin (5.9%). Amino acid analyses indicated that the CF mucin had higher levels of serine plus threonine (35%) as compared to the asthmatic mucin (29%). In contrast, CF mucin contained a lower content of aspartate, glutamate, and glycine than that observed for the asthmatic mucin. Molecular weights of 3.8 X 10(6) and 3.5 X 10(6) were obtained for CF and asthmatic mucins, respectively, from light-scattering studies of mucins in the presence of 6 M guanidine hydrochloride. Reduction of the disulfide bonds of the two mucins did not alter their molecular weights. Liquid chromatographic studies on Sepharose CL2B showed that CF mucin forms aggregates sufficiently large to be excluded from the gel. As compared to the CF mucin, the asthmatic mucin formed fewer of these large aggregates under identical experimental conditions. Reduction and alkylation of the mucins resulted in their inability to form aggregates. The higher state of aggregation of CF mucin may influence the viscoelastic properties of the CF lung's mucus secretions.

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The innervation of acini and ducts of eccrine sweat glands by immunoreactive, vasoactive intestinal peptide-containing nerve fibers was sharply reduced in seven patients with cystic fibrosis compared to eight normal subjects. The decrease in innervation by this neuropeptide, which has been shown to promote blood flow and the movement of water and chloride across epithelial surfaces in other systems, may be a basic mechanism for the decreased water content and relative impermeability of the epithelium to chloride and other ions that characterize cystic fibrosis.

The biophysical properties of purified native (nonreduced) mucus glycoproteins (mucins) isolated from lung mucus secretions of cystic fibrosis (CF) patients and subjects with normal lungs were studied using the technique of light scattering. The effects of different NaCl concentrations and 6 M guanidine hydrochloride on the molecular size of mucins, their ability to form aggregates, and their shape were investigated. Under the concentration range studied (0.05-3.5 mg/ml), in buffered 0.03 and 0.01 M NaCl, the CF mucins had higher molecular weights (12.2 x 10(6) to 17.1 x 10(6) and 9.5 x 10(6) to 10.4 x 10(6), respectively) than those observed in buffered 0.15 M NaCl (4.3 x 10(6) to 6.6 x 10(6]. These results were interpreted in terms of CF mucins self-aggregating in buffered 0.03 and 0.01 M NaCl. In contrast, in the both buffered 0.3 and 0.15 M NaCl, the normal respiratory mucins had molecular weights of 6.3 x 10(6) to 8.6 x 10(6), thus suggesting the absence of normal mucin aggregation in buffered 0.03 M NaCl. In the presence of 6 M guanidine HCl both CF and normal mucins had molecular weights of about 5 x 10(6) and showed more extended structure (i.e., larger radius of gyration) than in the presence of 0.03 or 0.15 M NaCl. Studies of the relationship of the light scattering intensity with scattering angle showed that, under the above experimental conditions studied, both CF and normal respiratory mucins were polydisperse flexible coil-shaped molecules. The increased aggregation of CF mucins observed at lower salt concentrations may alter the viscoelastic properties of CF lung mucus secretions.

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