Inhibition by wheat germ lectin, which amylase isoenzyme is inhibited?

• A. Salivary isoamylase
• B. Pancreatic isoamylase
• C. Muscle isoamylase
• D. Brain isoamylase

Answer: (A)

Wheat germ lectin binds to specific sugar residues on glycoproteins, and different isoforms of an enzyme can have distinct carbohydrate decorations. Amylase exists mainly as two human isoforms: one from the salivary glands and one from the pancreas. The salivary form carries glycan structures that wheat germ lectin recognizes, so when the lectin binds, it disrupts the enzyme’s structure or blocks its active site, inhibiting its activity. The pancreatic isoamylase has a different glycosylation pattern that isn’t affected by this lectin under the same conditions, so it remains active. Therefore, inhibition by wheat germ lectin identifies the salivary isoamylase as the inhibited enzyme.