Evaluation of WT and mutant enzymes
Assays were performed in this section with purified enzyme at a
fixed starting level of 40 U/mL. Therefore, similar protein amounts
of the WT and mutant enzymes were used. The stability of the
mutant was further investigated by measuring the half-life and
transition temperature (Tm). The half-life values for WT and BapulTS were 34.9 min and 387.3 min, respectively (increased 11-fold).
TheTmof Bapul-TS (74.5
◦
C) increased by 9.5
◦
C compared with that
of WT (65
◦
C) (Fig. 4A and B, respectively). These results indicated
that Bapul-TS had concomitant stabilizing effects on both kinetic
and thermodynamic stabilities. The optimum temperature and pH
were also investigated to determine whether the Bapul-TS activity was retained at 60
◦C and pH 5.0. Bapul-TS exhibited optimum
activity at 65
◦
C, which was 5
◦
C higher than the temperature at
which the WT exhibited optimum activity (60◦
C) (Fig. 4D). The
optimum pH of Bapul-TS was 5.0, and the profile of Bapul-TS was
nearly identical to that of WT (Fig. 4C). The specific activity of BapulTS remained relatively constant compared with that of the WT.