Which glycogen staining method is sensitive to diastase digestion?

• A. PAS
• B. Best carmine
• C. Bauer-feulgen
• D. Iodine method

Answer: (A)

The test is about whether a glycogen-staining method loses its signal after enzymatic digestion with diastase (alpha-amylase). Periodic acid–Schiff stains carbohydrates by oxidizing vicinal diols to aldehydes, which then react with Schiff reagent to produce a magenta color. Glycogen, with its abundant vicinal diols and branched structure, gives a strong PAS stain. When tissue is treated with diastase, glycogen is hydrolyzed and the substrate for the PAS reaction is removed, so the magenta color disappears. That diastase sensitivity is why PAS (especially PAS with diastase, PAS-D) is used to identify glycogen. Other stains may visualize glycogen or carbohydrates by different chemistries, but their signals aren’t defined by diastase digestion in the same diagnostic way.