2-硝基苯-beta-D-半乳糖苷 MSDS2-Nitrophenyl-beta-D-galactopyranoside
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 (K m ), turnover numbers (k cat ), and catalytic efficiencies (k cat /K m ) of Gal308 for ONPG and lactose are determined. The k cat and K m 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 k cat /K m value of the enzyme for ONPG (172.1 s -1 mM -1 ) is 4.6-fold higher than that for lactose (37.2 s -1 mM -1 ), which clearly demonstrated that the catalytic efficiency of Gal308 for ONPG is much higher than that for lactose.