Figure 5.

Folding kinetics of PGK and Ub*G. (A) PGK folds by a slow single exponential at 5°C, a faster stretched exponential at 19°C (Table 1) (t₁≈ 8 μs, t₂ ≈ 2 ms in χ₁ fit). (Inset) χ² for the fit to Eq. 1 is approximately constant, ruling out intermediates with a fluorescence signature not represented by a linear combination of the endpoints. (B) Ub*G folds by a slow single exponential at 2°C, a stretched exponential at 8°C. (Inset) The full 2°C χ₁ trace: an ≈20 μs phase attributed to D → D′ relaxation in the unfolded well precedes slow exponential folding (τ ≈ 5 ms) over a barrier. The fast initial phase has been subtracted from the 2°C trace in the main figure (t₁ ≈ 100, 3 and 1 μs in χ₁ fit for 2°C, 8°C, and Inset, respectively).