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Enzymatic Assay of Diamine Oxidase (E.C. No.

Document History

Replacing OP SPPUTR01. New document number assigned to conform to current document numbering system.

1. Objective

To standardize a procedure for the enzymatic assay of Diamine Oxidase.

2. Scope

This procedure applies to Sigma-Aldrich Product Number D7876, which has a specification for the enzymatic assay of Diamine Oxidase.

3. Definitions

3.1 Purified Water - water from a deionizing system, resistivity > or = 18MΩ•cm @ 25ºC

3.2. Unit Definition – One unit will oxidize 1.0 μmole of Putrescine per hour at pH 7.2 at 37ºC.

4. Discussion

Putrescine + H2O + O2   Diamine Oxidase   > 4 - Aminobutan aldehyde + NH3 + H2O2

H2O2 + o - DIANISIDIN e(reduced)   Peroxidase   > 2H2O + o - Dianisidin e(oxidized)

5. Responsibilities

It is the responsibility of all Analytical Services laboratory personnel to follow this protocol as written.

6. Safety

Refer to the Safety Data Sheet (SDS) for hazards and appropriate handling precautions.

7. Procedure

T = 37°C, pH = 7.2, A440nm, Light path = 1 cm

Spectrophotometric rate determination.


7.3.1     7.3.1. 100 mM Sodium Phosphate Buffer, pH 7.2 at 37ºC (Buffer)
Prepare a 12 mg/ml solution in purified water using Sodium Phosphate Monobasic, Sigma-Aldrich Product Number S0751. Adjust to pH 7.2 at 37ºC with 1 M NaOH.

7.3.2     75 mM Putrescine solution (Put)
Prepare a 12.1 mg/ml solution in reagent 7.3.1 using Putrescine Hydrochloride, Sigma-Aldrich Product Number P7505.

7.3.3     16 mM o-Dianisidine solution (ODA)
Prepare a 5 mg/ml solution using o-Dianisidine, Sigma-Aldrich Product Number F5803, in purified water. Prepare fresh and protect from light.    o-Dianisidine, Sigma-Aldrich Product Number D9154 (tablets), is not suitable for this assay.    o-Dianisidine is a known carcinogen, handle with care.

7.3.4.    Peroxidase Enzyme solution (POD)
Immediately before use prepare a solution containing 2000 pyrogallol units/ml in cold reagent 7.3.1(Buffer), using Peroxidase Type II from Horseradish, Sigma-Aldrich Product Number P8250.

7.3.5    Diamine Oxidase Enzyme solution (Enzyme)
Prepare a solution containing 3.0 to 6.0 units/ml of Diamine Oxidase in warm reagent 7.3.1 (37ºC). Incubate for 30 min at 37ºC before assaying to obtain complete enzyme dissolution.


7.4.1.    Pipette (in milliliters) the following reagents into suitable cuvettes:

  Test Blank
Reagent 7.3.1 (Buffer) 2.50 2.60
Reagent 7.3.2 (Put) 0.20 0.20
Reagent 7.3.3 (ODA) 0.10 0.10
Reagent 7.3.4 (POD) 0.10 0.10


7.4.2.    Mix by inversion and equilibrate to 37ºC. Monitor the A 440nm until constant, using a suitably thermostatted spectrophotometer. Then add:

Reagent 7.3.5(Enzyme) 0.10 ----


7.4.3.    Immediately mix by inversion and record the increase in A 440nm/min for 10 minutes.

7.4.4.    Obtain the maximum linear rate for both the Test and the Blank using a minimum of a 1.0 minute period and four A440nm points.


7.5.1 Units/ml enzyme = (ΔA440nm / minTest - ΔA440nm / min Blank)*(60)*(3.0)*(df)


     3.0 = volume (in milliliters) of assay
     60 = conversion factor from units/min to units/hour (Unit definition)
     df = Dilution factor
     11.3 = Millimolar extinction coefficient of oxidized o-Dianisidine at 440 m
     0.1 = Volume (in milliliters) of enzyme used

7.5.2 Units/mg solid = units/ml enzyme
mg solid/ml enzyme


7.5.3 Units/mg protein = units/ml enzyme
mg protein/ml enzyme



In a 3.0 ml reaction mix, the final concentrations are 96.7 mM Sodium Phosphate, 4.98 mM Putrescine, 0.53 mM o-Dianisidine, 200 units Peroxidase, and 0.3-0.6 units Diamine Oxidase.

8. References & Attachments

(1964) Nature 204, 1195.

9. Approval

Review, approvals and signatures for this document will be generated electronically using DocCompliance (QUMAS). Print a “For Use” copy if hardcopy with signature verification is required.


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