Which enzyme can be separated into five isoenzymes (LDH1–LDH5) by electrophoresis and exists in almost all tissues?

• A. Lipase
• B. Transaminase
• C. Creatine kinase
• D. Lactate dehydrogenase

Answer: (D)

The enzyme that fits this description is lactate dehydrogenase. Its pattern is five distinct isoenzymes, labeled LDH-1 through LDH-5, that can be separated by electrophoresis. This diversity comes from the enzyme’s structure: LDH is made of four subunits that can be either H (heart) or M (muscle), forming five combinations (H4, H3M, H2M2, HM3, M4) corresponding to the five isoforms. LDH is found in almost all tissues, reflecting its central role in converting pyruvate to lactate (and vice versa) during glycolysis and anaerobic metabolism. The other enzymes don’t show this classic five-isoenzyme electrophoretic pattern: lipase is mainly a single enzyme with limited isoforms, creatine kinase has three major forms, and transaminases have cytosolic and mitochondrial forms rather than five distinct bands.