Maltase Assay

Method: The enzymatic activity is determined by measuring the increase in absorbance at 400 nm caused by the hydrolysis of p-nitrophenyl-α-D-glucopyranoside. One unit hydrolyzes one umole of p-nitrophenyl-D-glucopyranoside (PNPG) at 37°C, pH 6.8, under the specified conditions.


  • 0.067 M Potassium phosphate, pH 6.8 with 0.001 M dithio-threitol (DTT).
  • 0.01 M p-nitrophenyl-α-D-glucopyranoside (PNPG). Substrate may be aliquoted into vials and frozen for future use. Once thawed, the substrate may not be re-frozen.


Dilute immediately before use in 0.067 M Potassium phosphate to obtain a rate of 0.02-0.04 ΔA/minute. The protein may be determined as follows:



Adjust spectrophotometer to 400 nm and 37°C and pipette into cuvettes as follows:

  Test Blank
Phosphate buffer 2.8 ml 2.9 ml
PNPG substrate 0.1 ml 0.1 ml

Incubate in spectrophotometer for 5-7 minutes to achieve temperature equilibrium and establish blank rate, if any. Add 0.1 ml diluted enzyme to test cuvette and mix. Record increase in A400 for 5-6 minutes. Calculate ΔA400/minute from the initial linear portion of the curve.



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