What is the purpose of adding LDH to the Walker/Karmen reagents?

• A. To prevent endogenous pyruvate from participating
• B. To produce NADH
• C. To inhibit other enzymes
• D. To stabilize the reaction

Answer: (A)

The key idea is preventing interference from any pyruvate already present in the sample. In the Walker/Karmen assay, pyruvate is quantified by a reaction that uses NADH; if endogenous pyruvate is around, it would also be consumed with NADH and falsely elevate the signal. Adding lactate dehydrogenase pretreats the sample by converting any existing pyruvate to lactate, so that only the pyruvate introduced for the assay (and measured via NADH consumption) contributes to the result. This keeps the measurement accurate.

It’s not about producing NADH (the LDH-catalyzed step actually consumes NADH), nor about inhibiting other enzymes or stabilizing the reaction.