1. Others
  2. Biochemical Assay Reagents
  3. ONPG

ONPG  (Synonyms: 2-Nitrophenyl β-D-galactopyranoside)

Cat. No.: HY-15926 Purity: 99.84%
COA Handling Instructions

ONPG is a colorimetric and spectrophotometric substrate for detection of β-galactosidase activity.

For research use only. We do not sell to patients.

ONPG Chemical Structure

ONPG Chemical Structure

CAS No. : 369-07-3

Size Price Stock Quantity
Solid + Solvent
10 mM * 1 mL in Water
ready for reconstitution
USD 33 In-stock
10 mM * 1 mL in Water USD 33 In-stock
500 mg USD 30 In-stock
1 g USD 40 In-stock
5 g USD 120 In-stock
10 g   Get quote  
50 g   Get quote  

* Please select Quantity before adding items.

This product is a controlled substance and not for sale in your territory.

Customer Review

Based on 4 publication(s) in Google Scholar

Other Forms of ONPG:

Top Publications Citing Use of Products
  • Biological Activity

  • Protocol

  • Purity & Documentation

  • References

  • Customer Review


ONPG is a colorimetric and spectrophotometric substrate for detection of β-galactosidase activity.

In Vitro

The enzyme displays high hydrolysis ability for ONPG (100%) and moderate activity for its natural substrate lactose (25.7%). However, the hydrolysis ability of the enzyme towards all other chromogenic nitrophenyl analogues is very weak, indicating that Gal308 is a β-galactosidase with narrow substrate specificity. To investigate the kinetic parameters of recombinant enzyme, the Michaelis-Menten constants (Km), turnover numbers (kcat), and catalytic efficiencies (kcat/Km) of Gal308 for ONPG and lactose are determined. The kcat and Km values are 464.7±7.8 s-1 and 2.7±0.3 mM for ONPG, and 264.2±2.1 s-1 and 7.1±0.8 mM for lactose, respectively. The kcat/Km value of the enzyme for ONPG (172.1 s-1mM-1) is 4.6-fold higher than that for lactose (37.2 s-1mM-1), which clearly demonstrated that the catalytic efficiency of Gal308 for ONPG is much higher than that for lactose[1].

MedChemExpress (MCE) has not independently confirmed the accuracy of these methods. They are for reference only.

Molecular Weight







White to off-white




Room temperature in continental US; may vary elsewhere.

Powder -20°C 3 years
4°C 2 years
In solvent -80°C 2 years
-20°C 1 year
Solvent & Solubility
In Vitro: 

H2O : 8.33 mg/mL (27.65 mM; ultrasonic and warming and heat to 60°C)

Stock Solutions
Concentration Solvent Mass 1 mg 5 mg 10 mg
1 mM 3.3195 mL 16.5975 mL 33.1950 mL
5 mM 0.6639 mL 3.3195 mL 6.6390 mL
10 mM 0.3320 mL 1.6598 mL 3.3195 mL
*Please refer to the solubility information to select the appropriate solvent.
Purity & Documentation

Purity: 99.84%

Kinase Assay

The β-galactosidase activity is measured using two substrates including ONPG and lactose in this study. The β-galactosidase activity for ONPG is measured by following the amount o-nitrophenol released from ONPG. The reaction mixture is composed of 100 μL of the enzyme solution and 400 μL of ONPG solution (2.5 g/L in 100 mM Tris-HCl buffer at pH 6.8). After incubation at 78°C for 15 min, the reaction is terminated by adding an equal volume of 1 M Na2CO3. The released o-nitrophenol is quantitatively determined by measuring at A405. One unit of activity is defined as the amount of enzyme needed to produce 1 μmol of o-nitrophenol per minute under the assay condition. The specific activity is expressed as units per milligram of protein. Assays for activity towards lactose are performed in the same buffer containing 100 μL of enzyme solution and 5% lactose, and the reaction is stopped by boiling for 10 min, and the concentration of glucose is determined using a glucose oxidase-peroxidase assay kit. The released glucose is quantitatively determined by measuring A492. One unit of enzyme activity is defined as the amount of activity required to release 1 μmol of glucose per minute[1].

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

  • No file chosen (Maximum size is: 1024 Kb)
  • If you have published this work, please enter the PubMed ID.
  • Your name will appear on the site.

ONPG Related Classifications

Help & FAQs
  • Do most proteins show cross-species activity?

    Species cross-reactivity must be investigated individually for each product. Many human cytokines will produce a nice response in mouse cell lines, and many mouse proteins will show activity on human cells. Other proteins may have a lower specific activity when used in the opposite species.

  • Molarity Calculator

  • Dilution Calculator

The molarity calculator equation

Mass (g) = Concentration (mol/L) × Volume (L) × Molecular Weight (g/mol)

Mass   Concentration   Volume   Molecular Weight *
= × ×

The dilution calculator equation

Concentration (start) × Volume (start) = Concentration (final) × Volume (final)

This equation is commonly abbreviated as: C1V1 = C2V2

Concentration (start) × Volume (start) = Concentration (final) × Volume (final)
× = ×
C1   V1   C2   V2

Your Recently Viewed Products:

Inquiry Online

Your information is safe with us. * Required Fields.

Product Name



Applicant Name *


Email Address *

Phone Number *


Organization Name *

Department *


Requested quantity *

Country or Region *



Bulk Inquiry

Inquiry Information

Product Name:
Cat. No.:
MCE Japan Authorized Agent: