Cobalamin R binder as a possible model molecule for glycoprotein study in cystic fibrosis.

The isoprotein pattern of semi-purified R binder (an acidic glycoprotein which binds cobalamin) from saliva and sera of 8 cystic fibrosis patients was compared to that of R binder from samples of 5 healthy children. In cases of cystic fibrosis, the mean isoelectric point of salivary R binder was increased from 3.78 up to 4.34 and its microheterogeneity was reduced. These significant physicochemical modifications were not observed with R binder from cystic fibrosis sera and they did not correlate with the beta-galactosidase, alpha-mannosidase, alpha-L-fucosidase nor neuraminidase activity of saliva. We propose the R binder as a model molecule to study the glycoprotein metabolism in cystic fibrosis since it contains 30-40% carbohydrate, is easily complexed with cyano[57Co]cobalamin and is present in most tissues and fluids of the human organism.