HomeEnzyme Activity AssaysAssay Procedure for Protease

Assay Procedure for Protease


Alkalophic proteinase

The appearance of peptides is measured as tyrosine equivalent at 275 nm by spectrophotometry.

Unit definition

One unit causes the increase of optical density at 275 nm corresponding to one micromole of tyrosine per minute under the conditions described below.




  1. Pipette 3.0 mL of substrate solution (A) into a test tube and equilibrate at 30 ℃ for 5 minutes.
  1. Add 0.5 mL of the enzyme solution* and mix.
  2. After exactly 10 minutes at 30 ℃, add 3.2 mL of TCA mixture (B) to stop the reaction.
  3. Incubate for further 20 minutes at 30 ℃.
  4. Filter the mixture with a filter paper (Toyo Roshi No.131) and measure the optical density of the filtrate at 275 nm (OD test).

At the same time, prepare the blank by first mixing the substrate solution with 3.2mL of TCA mixture (B) after 10 min-incubation at 30 ℃, followed by addition of the enzyme solution, and carry out the same procedure (procedure 4-5) at test (OD blank).

* Dissolve the enzyme preparation in ice-cold 10 mM borax-NaOH buffer, pH 11.0 and dilute to 0.1-0.4U/mL with enzyme diluent (C), immediately before assay.


Activity can be calculated by using the following formula:

Volume activity

Weight activity (U/mg)=(U/mL)×1/C

This procedure is for informational purposes.

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