Table 4.
Solvent Isotope Effects on Fluorescence Quenching in Hairpin Peptides. a
| Substitutions | pH | kq(H2O) / (108 s−1) b | kq(D2O) / (108 s−1) b | kq(H2O)/kq(D2O) |
|---|---|---|---|---|
| none | 6.5 | (0) c | 0.18 ± 0.02 | c |
| Ala8Asp | 3.0 | 3.85 ± 0.16 | 2.79 ± 0.23 | 1.4 ± 0.1 |
| Ala8Glu | 3.0 | 1.63 ± 0.22 | 1.63 ± 0.17 | 1.0 ± 0.2 |
| Ala8His | 3.0 | 5.09 ± 0.14 | 4.82 ± 0.62 | 1.1 ± 0.1 |
| Phe10His | 3.0 | 9.31 ± 0.41 | 5.29 ± 0.40 | 1.8 ± 0.2 |
| Ala8Orn | 6.5 | 2.63 ± 0.13 | 0.28 ± 0.03 | 9.3 ± 1.1 |
| Ala8Tyr | 6.5 | 2.09 ± 0.08 | 1.22 ± 0.08 | 1.7 ± 0.2 |
| 11.5 d | 16.1 ± 0.71 | 12.7 ± 1.1 | 1.3 ± 0.1 | |
| Phe10Tyr | 6.5 | 1.21 ± 0.08 | 0.70 ± 0.19 | 1.7± 0.2 |
| 11.5 d | 30.8 ± 1.9 | 16.5 ± 4.6 | 1.9 ± 0.6 | |
| Ala8Cys | 6.5 | 14.5 ± 0.62 | 8.02 ± 0.41 | 1.8 ± 0.2 |
| 10.0 | 2.86± 0.09 | 2.20 ± 0.09 | 1.2 ± 0.1 |
a
The peptides are Ac-WVTIpGKAIFTG-NH2 with the indicated substitutions for residues in bold font.
b
Rate constant for the pH-dependent quenching process in H2O or D2O, all at 295 K except for the Ala8/His10 peptide, which was measured at 285 K. Calculated as described in the text except for Ala 8. The entries are the mean and standard deviation of three measurements.
c
The fluorescence yield for Ala8 was independent of pH, and was not significantly affected by deuteration of the solvent: ϕ(H2O) was 0.25 ± 0.01 and ϕ(D2O) was 0.26 ± 0.02.
d
Tyr probably is not completely deprotonated at this pH.