Ascorbic acid oxidase is a metalloenzyme. Which metallic ion is an integral part of its active site?

Introduction:
Many oxidoreductases require metal ions as cofactors for electron transfer. Ascorbic acid oxidase catalyzes the oxidation of ascorbic acid (vitamin C) to dehydroascorbic acid. Knowing the specific metal center helps understand its catalytic mechanism and spectroscopic properties.

Given Data / Assumptions:

• Target enzyme: ascorbic acid oxidase.
• We are to identify the metal cofactor.
• Typical redox metals include Cu, Fe, Mn among others.

Concept / Approach:
Ascorbic acid oxidase is a blue copper protein. Copper ions in the active site mediate electron transfer from ascorbate to molecular oxygen. The distinct spectroscopic signature (blue color) is associated with type 1 copper centers in such enzymes.

Step-by-Step Solution:
Step 1: Recall the classification of blue copper oxidases.Step 2: Recognize ascorbic acid oxidase as a copper-dependent enzyme.Step 3: Select the metal ion Cu from the options.

Verification / Alternative check:
Biochemistry references consistently describe ascorbic acid oxidase as containing copper at its catalytic center, explaining its redox cycling and spectral features.

Why Other Options Are Wrong:

• Mg: Typically structural/ATP-related; not a redox center here.
• Fe: Present in heme or iron-sulfur enzymes; not characteristic of this oxidase.
• Mn: Occurs in specific oxidases but not in ascorbic acid oxidase.
• Zn: Common in hydrolases; not the redox cofactor required.

Common Pitfalls:
Confusing copper-containing oxidases with iron-containing peroxidases; overlooking the hallmark “blue copper” description tied to Cu centers.

Final Answer:
Cu