Which substrate is used in the Bowers-McComb method for ALP?

• A. β-Glycerophosphate
• B. p-Nitrophenyl phosphate
• C. Phenylphosphate
• D. α-Naphthyl phosphate

Answer: (B)

Alkaline phosphatase assays rely on a substrate that yields a colorimetric product directly when cleaved. In the Bowers-McComb method, the substrate used is p-nitrophenyl phosphate. Upon hydrolysis by ALP, p-nitrophenyl phosphate releases p-nitrophenol, which in alkaline solution becomes p-nitrophenolate and has a strong yellow color with absorbance at 405 nm. This allows straightforward spectrophotometric measurement of enzyme activity in a single step. Other substrates like β-glycerophosphate, phenyl phosphate, or α-naphthyl phosphate do not give a simple, directly measurable color change in this method, or require extra steps, so they’re not used here.