Which of the following is NOT a coenzyme involved in the lactate dehydrogenase assay?

• A. NAD/NADH
• B. ATP/ADP
• C. Fe++/Fe+++
• D. Cu/Cu++

Answer: (B)

The lactate dehydrogenase (LDH) assay relies on the enzyme-catalyzed reaction where lactate is oxidized to pyruvate with the concurrent reduction of NAD+ to NADH. The presence of NAD+/NADH as the electron carrier is essential, and the assay measures NADH formation (often by its absorbance at 340 nm). ATP/ADP is not part of this redox chemistry; it’s a nucleotide involved in energy transfer in other pathways but does not serve as the coenzyme for the LDH-catalyzed step. The metal ions Fe++/Fe+++ and Cu/Cu++ are inorganic cofactors in various enzymes, but LDH does not require them as coenzymes in this assay. Therefore, ATP/ADP is the component not involved as a coenzyme in the LDH assay.