Figure 2. Thermostability of TPP1 preparations.

Left Panels: Proenzyme was incubated at pH 7.2 at different temperatures and then frozen at the indicated times. Preparations were subsequently autoactivated at pH 3.5 for 1.5 h at 37°C prior to measuring enzyme activity. Right Panels: Proenzyme was autoactivated prior to incubation at pH 4.5 at the indicated times and temperatures and then frozen prior to directly measuring TPP1 enzyme activity. Results (mean and standard deviation of duplicate determinations) are normalized to the activity of enzyme incubated at 4°C. Unmodified TPP1, open circles and bars; OX-TPP1, filled circles and bars, DG-TPP1, gray squares and bars. The concentration of enzyme during incubation was 0.1 mg/ml.