What is the colored reaction product formed in the Reitman Frankel method (denoted as brown)?

• A. 2,4-Dinitrophenylhydrazone
• B. NADH
• C. Malate
• D. Lactate

Answer: (A)

This question focuses on the color-forming product in the Reitman-Frankel alanine aminotransferase (ALT) assay. After ALT converts alanine to pyruvate, the pyruvate reacts with 2,4-dinitrophenylhydrazine in strongly acidic conditions to form the 2,4-dinitrophenylhydrazone derivative. This hydrazone is the brown-colored compound that’s measured spectrophotometrically. So the colored product is the 2,4-dinitrophenylhydrazone of pyruvate. NADH, malate, and lactate are not involved in producing this brown color in this method.