Counter-ion binding to mucus glycoproteins

The affinity of pig gastric mucus glycoprotein for counter ions of various valencies was examined. Ions of higher valency were bound with increasing avidity, but the degree of binding was apparently not influenced by the ionic radius. The affinity of the glycoprotein for the ions studied may be ranked: Fe3+ greater than Al3+ greater than Ca2+ greater than Cs+ congruent to Na+. The binding of calcium was inhibited by high ionic strength and was sensitive to the pH of the environment. Enzymatic removal of sialic acid slightly reduced the calcium binding capacity.