Trace minerals — Which mineral primarily supports protein metabolism and functions as a cofactor in oxidation–reduction (redox) reactions within antioxidant enzymes?

Introduction / Context:
Several trace minerals act as enzyme cofactors in metabolism. One mineral is notable for roles in amino acid and protein metabolism, bone formation, and as a catalytic component of key redox enzymes, including a mitochondrial form of superoxide dismutase. This question asks you to identify that mineral.

Given Data / Assumptions:

• Protein metabolism involves urea cycle and amino acid–modifying enzymes.
• Antioxidant defense relies on superoxide dismutases and other redox enzymes.
• Trace minerals can be enzyme-bound at active sites.

Concept / Approach:
Manganese serves as a cofactor for multiple enzymes: Mn-superoxide dismutase (MnSOD) in mitochondria (redox defense), arginase (urea cycle; protein nitrogen handling), and pyruvate carboxylase, among others. While molybdenum is also a redox cofactor (xanthine oxidase, sulfite oxidase), it is less associated with protein metabolism per se. Magnesium broadly stabilizes ATP and nucleotides but is not specifically a protein-metabolism/redox cofactor in the same way, and calcium is chiefly signaling/structural.

Step-by-Step Solution:

Verification / Alternative check:
Biochemical assays localize MnSOD to the mitochondrial matrix; genetic loss or dietary deficiency impairs oxidative stress handling and can alter nitrogen metabolism, consistent with manganese’s dual functional profile.

Why Other Options Are Wrong:

• Molybdenum: important in oxidases but not primarily in protein metabolism.
• Magnesium: ubiquitous ATP cofactor, not a targeted redox/protein metabolism match.
• Calcium: signal transduction and bone mineral; not an oxidation–reduction enzyme cofactor.
• Zinc: many enzymes (including in protein metabolism), but the redox enzyme hallmark specified here (MnSOD) contains manganese, not zinc.

Common Pitfalls:
Equating “redox cofactor” only with molybdenum or iron. The mitochondrial SOD specifically uses manganese, a distinctive clue embedded in the question.

Final Answer:
Manganese.