Carboxylated mucins after Alcian Blue technique at pH 1.0 show which result?

• A. No demonstration - not blue
• B. Blue
• C. Green
• D. Red

Answer: (A)

The key idea is how pH controls which acidic groups Alcian Blue can bind. Alcian Blue is a positively charged dye that sticks to negatively charged acidic mucins. At very low pH (1.0), the carboxyl groups on carboxylated mucins are protonated (COOH) and lose their negative charge. Without that negative charge, the dye cannot bind these mucins, so they do not stain blue. Therefore, carboxylated mucins would show no staining at pH 1.0. (Sulfated mucins would still stain blue under these conditions because sulfate groups remain negatively charged.)