Which mucin type remains demonstrated after hyaluronidase digestion with Alcian blue 1.0?

• A. Glycoproteins
• B. Hyaluronic acid
• C. Chondroitin sulfate A
• D. Sulfated mucosubstances

Answer: (A)

Alcian blue staining at a very acidic pH highlights acidic groups in mucins, especially sulfated and carboxylated residues. Hyaluronidase specifically digests hyaluronic acid, a non-sulfated glycosaminoglycan that can be a component of mucins. When tissue is treated with hyaluronidase, the hyaluronic acid–rich portions of mucins are removed, so staining that depended on those components diminishes or disappears. Glycoprotein mucins, on the other hand, have protein cores with carbohydrate chains that can carry acidic groups (such as sulfates or sialic acids) and are not degraded by hyaluronidase. Therefore, after hyaluronidase digestion, Alcian blue 1.0 still binds to these glycoprotein mucins, making them the remaining detectable type.