Alcian Blue 1.0 is specific for which group of mucopolysaccharides?

• A. Sulfated (only) acid mucopolysaccharides
• B. Carboxylated acid mucopolysaccharides
• C. Neutral polysaccharides
• D. Glycogen

Answer: (A)

Alcian Blue staining is driven by the negative charges on acidic mucopolysaccharides. The dye is cationic, so it binds where there are sulfates or carboxyl groups, but the exact groups that bind depend on the pH used.

At a very low pH (about 1.0), only the strongly sulfated mucopolysaccharides carry enough negative charge to attract the dye, so Alcian Blue 1.0 stains sulfated acid mucopolysaccharides specifically. Carboxylated mucopolysaccharides, while acidic, don’t bind under this highly acidic condition, so they aren’t stained at this pH. Neutral polysaccharides and glycogen lack these charged groups and therefore do not stain with Alcian Blue at this pH.

If the pH were raised to around 2.5, both sulfated and carboxylated mucopolysaccharides would stain, which explains why the pH 1.0 variant is selective for sulfated groups. Hence, Alcian Blue 1.0 is best described as specific for sulfated acid mucopolysaccharides.