Fig. 3.

Thermostability of PutA. Full-length PutA (2 mg/ml) and PutA86–630 (2 mg/ml) were incubated in 50 mM potassium phosphate buffer (pH 7.5) containing 50 mM NaCl at 45 °C. At the indicated time points protein samples were removed from the heating mixture and assayed for PRODH activity using the proline:oxidoreductase DCPIP assay as previously described (Becker and Thomas, 2001). Assay results for PutA (closed circles) and PutA86–630 (open circles) are reported as relative percent activity based on the initial PRODH activity at 0 min. A rate constant of 0.18 ± 0.03 min⁻¹ was estimated for the decay in PRODH activity with full-length PutA using best-fit analysis to a single exponential equation. PutA and PutA86–630 were purified as described (Zhu and Becker, 2005; Zhang et al., 2007).