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MBBS QUESTION #10322
Question 1
Isoenzymes (isozymes), such as the five tissue-specific forms of lactate dehydrogenase (LDH1-LDH5), are clinically useful in diagnosis because they:
  • Catalyze entirely different chemical reactions depending on the tissue of origin
  • Catalyze the same reaction but have distinct tissue distributions, so their relative serum pattern can help localize the site of tissue damage✔️
  • Differ only in molecular weight, with no diagnostic significance
  • Are found exclusively intracellularly and are never released into serum after tissue injury
Correct Answer Explanation
Isoenzymes share catalytic function but differ in subunit composition and tissue distribution (e.g., LDH1 predominates in cardiac muscle and red blood cells, LDH5 in liver and skeletal muscle); a shift in the serum LDH isoenzyme pattern after tissue injury can help identify the likely site of damage.