Which substance is used as the substrate when performing amylase activity assays?

• A. Starch
• B. Glycogen
• C. Raffinose
• D. Cellulose

Answer: (A)

Amylase acts by breaking the alpha-1,4 glycosidic bonds in starch, turning a large polysaccharide into smaller maltose and glucose units. For activity assays, starch is used as the substrate because it directly represents what amylase naturally digests and provides a measurable change as it is degraded. The assay often tracks either the disappearance of intact starch (for example with iodine binding) or the appearance of reducing sugars produced by hydrolysis (using reagents like DNS). Other substances listed don’t fit because glycogen, while a glucose polymer, is more branched and not the standard substrate for typical amylase assays; raffinose is a small sugar not targeted by amylase, and cellulose is built from beta-1,4 linkages that amylase cannot hydrolyze.