α-Amylase is an endo-acting starch-hydrolysing enzyme that requires which divalent ion for structural stability and optimal catalytic activity?

Introduction:
α-Amylase is a key endo-enzyme in starch processing, bakery, and brewing. It cleaves internal α-1,4-glycosidic linkages in amylose and amylopectin, rapidly reducing viscosity and producing dextrins. Its activity and stability are strongly influenced by bound metal ions.

Given Data / Assumptions:

• Enzyme: α-amylase (endo-acting).
• Question focuses on essential metal requirement.
• Options include Ca, Cu, Mn, and None of these.

Concept / Approach:
Most α-amylases possess a tightly bound Ca2+ at specific sites that stabilizes tertiary structure, helps maintain the active site geometry, and increases thermal tolerance. Without Ca2+, the enzyme loses rigidity and becomes susceptible to denaturation, reducing catalytic efficiency under process conditions.

Step-by-Step Solution:

Verification / Alternative check:
Industrial practice often supplements process streams with Ca2+ (for example, in liquefaction) to preserve enzyme performance at elevated temperatures. Chelating agents like EDTA reduce activity by stripping Ca2+, demonstrating the requirement experimentally.

Why Other Options Are Wrong:

• Cu: Not a structural requirement for α-amylase; excess Cu2+ may even inhibit enzymes.
• Mn: Some enzymes use Mn2+, but α-amylase classically depends on Ca2+.
• None of these: Incorrect because Ca2+ requirement is well established.

Common Pitfalls:
Confusing α-amylase with enzymes like polyphenol oxidase or tyrosinase that require Cu. Another mistake is assuming all hydrolases are metal independent; α-amylase is a clear counterexample due to its Ca-binding architecture.

Final Answer:
Ca