Mucin is precipitated by acetic acid except for which mucin?

• A. Gastric mucin
• B. Intestinal mucin
• C. Colonic mucin
• D. Bronchial mucin

Answer: (A)

The test hinges on how mucins respond to acetic acid based on their chemical makeup. Mucins that carry more acidic groups—such as sialic acid or sulfate—tend to lose solubility when exposed to acetic acid, promoting precipitation as the molecules interact and aggregate. Gastric mucin, however, is predominantly neutral in charge and contains fewer acidic groups compared with intestinal, colonic, and bronchial mucins. Because of this, gastric mucin remains soluble in acetic acid and does not precipitate, making it the exception.