Strongly sulfated mucins (chondroitin sulfate and heparin sulfate) are stained by which reagent?

• A. Colloidal iron
• B. Alcian blue
• C. PAS
• D. Mucicarmine

Answer: (A)

Strongly sulfated mucins carry many sulfate groups, giving them a pronounced negative charge. Colloidal iron staining uses iron-containing colloids that bind to these negatively charged sulfate groups, producing a vivid deposit in mucin-rich areas. This makes colloidal iron particularly sensitive for sulfated mucopolysaccharides like chondroitin sulfate and heparan sulfate. While Alcian blue also stains acidic mucins, its scope includes a broader range of acidic mucins and depends on pH, so it’s less specific for the degree of sulfation. PAS and mucicarmine target neutral mucins or other mucin components rather than sulfated ones. Therefore, colloidal iron is the best reagent to reveal strongly sulfated mucins.