Isoenzymes (isozymes): which description best defines them in biochemical terms?

Introduction / Context:
Many organisms express multiple enzyme variants that catalyze the same chemical reaction. These isoenzymes provide tissue specificity, developmental regulation, and diagnostic markers (for example, LDH and CK isoforms in clinical chemistry).

Given Data / Assumptions:

• We need the definition that captures structure versus function.
• Isoenzymes should catalyze the same reaction but may differ in protein sequence or quaternary structure.

Concept / Approach:
Isoenzymes (isozymes) are distinct molecular forms of an enzyme (different amino acid sequences or subunit compositions) that catalyze the same biochemical reaction, often with different kinetic properties or regulation. They are not “the same structural form”; they are structurally different but functionally equivalent with respect to the reaction catalyzed.

Step-by-Step Solution:

Verification / Alternative check:
Classic examples: LDH isoenzymes (H and M subunits) forming tetramers with distinct tissue distribution but catalyzing lactate ↔ pyruvate.

Why Other Options Are Wrong:

• Same structural forms: contradicts “iso.”
• Catalyzes oxidation reactions: describes an enzyme class (oxidoreductases) rather than isoenzyme concept.
• None of these: incorrect because a correct definition is provided.

Common Pitfalls:
Thinking “identical catalytic properties” means identical kinetics; in practice, they catalyze the same reaction but kinetics/regulation may differ. The key is reaction identity.

Final Answer:
have different structural forms but identical catalytic properties