Salivary Mucins of Patients with Cystic Fibrosis: Composition and susceptibility to degradation by salivary glycosidases

When human saliva is incubated at 37 C, the protein-bound carbohydrates of salivary mucins are rapidly released under the action of exoglycosidases of bacterial and glandular origin. When salivas of patients with cystic fibrosis and of matched control subjects were compared in this respect, the release of protein-bound carbohydrate from cystic saliva was appreciably slower than from normal saliva. This abnormal behavior of cystic saliva during incubation does not appear to be due to a deficiency of cystic saliva in exoglycosidases. The activities of neuraminidase, β-galactosidase, β-N-acetylglucosaminidase, α-l-fucosidase, and α-d-mannosidase in cystic and normal salivas were assayed against artificial substrates and were found to be on the whole similar. These observations suggest that the abnormal accumulations of mucins in certain tissues and organs in cystic fibrosis could be due to a lowered susceptibility of cystic mucins to enzymatic degradation.