Which method is colorimetric-spectrophotometric for transaminase determination?

• A. Reitman Frankel
• B. Karmen/AST or Walker/ALT
• C. Both
• D. Neither

Answer: (A)

Colorimetric-spectrophotometric transaminase assays work by turning the enzyme’s activity into a colored signal that can be measured. In the Reitman-Frankel approach, the transaminase transfers an amino group from an amino acid to an α-keto acid (aspartate to oxaloacetate for AST, or alanine to pyruvate for ALT). The resulting keto acids are then reacted with 2,4-dinitrophenylhydrazine to form colored hydrazones. After a color-developing step, the intensity of the color is read spectrophotometrically around 505 nm and is proportional to enzyme activity. This makes it a classic colorimetric-spectrophotometric method for determining transaminases. Other named methods (like Karmen or Walker) exist and are also colorimetric, but Reitman-Frankel is the standard reference taught for this type of assay, which is why it’s the best answer here.