Enzyme thermal stability experiments showed that the enzymes remained more than 80% residual activity at 45uC and 55uC for 120 min heat treatment, respectively ( Figure 5C and 5D) . At 65uC, the residual activity of AtGUS(-3t)-E remained almost 60% of enzymatic activity after 30 min heat treatment, which was comparatively higher than that of AtGUS-E with less than 5% residual activity after the same treatment. At a higher temperature (75uC), both enzyme residual activity rapidly vanished, and within 15 min heat treatment, almost all enzymatic activity was lost.