Figure 4.

Kinetics of cytochrome c folding in the presence and absence of imidazole following dilution of chemical denaturant. Cytochrome c in 4.4 M Gdn·HCl (0.2 M imidazole/0.1 M potassium phosphate buffer, pH 7) was diluted 6-fold with buffer (0.2 M imidazole/0.1 M potassium phosphate, pH 7) to a final Gdn·HCl concentration of 0.7 M at 20°C. The total fluorescence intensity at wavelengths longer than 320 nm was measured relative to tryptophan, and has been scaled as described in the text. The values at negative times indicate the expected intensity at zero time, calculated by correcting the intensity at 4.4 M Gdn·HCl for the influence of Gdn·HCl as determined from the nonapeptide. The intensity at 0.7 M Gdn·HCl for the 1–65 fragment is 0.4 (7). The lines show exponential fits to the data, with relaxation times of 1.6 ms (solid line) and 10.9 ms (broken line).