The contribution of associated and covalently bound lipids to the viscosity of gastric mucus glycoprotein in healthy and cystic fibrosis (OF) individuals was investigated. While both preparations exhibited similar contents of protein and carbohydrate, the CF glycoprotein contained 1.3 times more associated lipids and 6 times more covalenlly bound fatty acids. The viscosity of CF mucus glycoprotein was aboul 1.8 limes higher than that of normal glycoprotein. Extraction of associated lipids lead to 3-fold drop in the viscosity of CF glycoprotein and 5-fold drop in the case of normal glycoprotein. Removal ofcovalcntly bound fatty-acids caused further 1.6-fold reduction in the viscosity of normal mucus glycoprotein and 6-fold in CF glycoprotein. The viscosity of the delipidated and deacylatcd CF mucus glycoprotein was only about 10% higher than that of the similarly treated normal glycoprotein. The results suggest that the elevated level of covalently bound and associated lipids is responsible for the increased viscosity of CF mucin.
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