Which color is produced by the chromogenic product in the ALP assay under alkaline conditions?

Which color is produced by the chromogenic product in the ALP assay under alkaline conditions?

• A. Yellow
• B. Blue
• C. Red
• D. Green

Answer: (A)

Alkaline phosphatase activity is detected using a substrate that becomes a colored product when hydrolyzed in alkaline conditions. The substrate p-nitrophenyl phosphate is converted to p-nitrophenol by the enzyme, and at high pH this product loses a proton to form p-nitrophenolate, which has a yellow color. That yellow chromogenic product is what’s measured to indicate enzyme activity. Blue, red, or green would come from different chromogenic systems not produced by this ALP reaction under alkaline conditions.

Alkaline phosphatase activity is detected using a substrate that becomes a colored product when hydrolyzed in alkaline conditions. The substrate p-nitrophenyl phosphate is converted to p-nitrophenol by the enzyme, and at high pH this product loses a proton to form p-nitrophenolate, which has a yellow color. That yellow chromogenic product is what’s measured to indicate enzyme activity. Blue, red, or green would come from different chromogenic systems not produced by this ALP reaction under alkaline conditions.