Catalytic activity and stabilization of phenyl-modified glucose oxidase at high hydrostatic pressure

Glucose oxidase (GOx) was modified by attaching phenyl groups to either carboxyl or amino side chains on the enzyme. High hydrostatic pressure (HHP) stabilized the aniline-, and benzoate-modified GOx at 69.1-80 °C compared to atmospheric pressure. At 240 MPa and 80.0 °C, the first order rate constant of inactivation k_inact. of aniline-modified GOx was 20 × 10^-2 min^-1, or 3.7 times smaller than for the native GOx, while the k_inact for benzoate-modified GOx was 26 × 10^-2 min^-1, or 2.8 times smaller than for the native GOx at the same temperature. Furthermore, at 240 MPa and 80.0 °C, the k_inact of the aniline-modified GOx was 69 times smaller than the k_inact of native GOx (1530 × 10^-2 min^-1) at 0.1 MPa and 80.0 °C. Similar results were obtained for benzoate-modified GOx. At each temperature in this study (25-69.1 °C), the catalytic activity of the native, aniline-, or benzoate-modified GOx increased with HHP, and reached a maximum at around 180 MPa. At 180 MPa and 69.1 °C, aniline-modified GOx produced the fastest catalytic rate, followed by benzoate-modified GOx, and then native GOx. An increase in temperature increased the activation volume of the reaction. Similarly, the activation energy increased with pressure. The combination of HHP and hydrophobic modification made GOx more thermostable and increased the effect of temperature in enzyme activity.