ONPGONPG
MedChemExpress (MCE)
HY-15926
369-07-3
2-Nitrophenyl β-D-galactopyranoside
99.84%
Powder -20°C 3 years 4°C 2 years In solvent -80°C 2 years -20°C 1 year
Room temperature in continental US
may vary elsewhere.
ONPG is a colorimetric and spectrophotometric substrate for detection of β-galactosidase activity.
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].
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].
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[1]. Zhang X, et al. Metagenomic approach for the isolation of a thermostable β-galactosidase with high tolerance of galactose and glucose from soil samples of Turpan Basin. BMC Microbiol. 2013 Oct 24
13:237. doi: 10.1186/1471-2180-13-237. [Content Brief]