TABLE 3.
Peptides treated with β-propiolactone at different pH values
| Peptide | Sequence | Mass | Adductsa | ΔMb | Conversionc |
|||
|---|---|---|---|---|---|---|---|---|
| pH 3.0 | pH 5.0 | pH 7.0 | pH 9.0 | |||||
| Da | Da | % | ||||||
| 1 | Ac-VTLAVTR-NH2 | 799.492 | 0d | –e | –e | – | – | 0.3 ± 0.1 |
| 2 | Ac-VTLCVTR-NH2 | 831.464 | 4 | 72/144 | – | 8.4 ± 2.2 | 98.5 ± 0.4 | 98.6 ± 00 |
| 3 | Ac-VTLDVTR-NH2 | 843.481 | 2 | 72/144 | 1.8 ± 0.3 | 4.2 ± 0.2 | 9.2 ± 1.2 | 8.0 ± 0.7 |
| 4 | Ac-VTLEVTR-NH2 | 857.497 | 2 | 72/144 | 0.8 ± 0.1 | 2.8 ± 0.1 | 7.7 ± 1.1 | 10.8 ± 2.3 |
| 5 | Ac-VTLHVTR-NH2 | 865.513 | 2 | 72/144 | – | 0.3 ± 0.0 | 15.5 ± 0.4 | 25.0 ± 0.7 |
| 6 | Ac-VTLKVTR-NH2 | 856.549 | 2 | 72 | – | – | 0.7 ± 0.2 | 5.8 ± 0.4 |
| 7 | Ac-VTLMVTR-NH2 | 859.495 | 2 | 72/144 | 58.7 ± 2.8 | 50.7 ± 3.2 | 37.6 ± 1.2 | 36.4 ± 4.0 |
| 8 | Ac-VTLNVTR-NH2 | 842.497 | 0 | – | – | – | – | 0.5 ± 0.1 |
| 9 | Ac-VTLQVTR-NH2 | 856.513 | 0 | – | – | – | – | 1.0 ± 0.1 |
| 10 | Ac-VTLSVTR-NH2 | 815.487 | 1 | 72 | – | – | 0.2 ± 0.0 | 2.2 ± 0.1 |
| 11 | Ac-VTLWVTR-NH2 | 914.534 | 0 | – | – | – | – | 0.2 ± 0.0 |
| 12 | Ac-VTLYVTR-NH2 | 891.518 | 1 | 72 | – | – | 2.7 ± 0.1 | 14.7 ± 0.3 |
a The number of β-propiolactone adducts attached to the residue in bold (X) are given in bold. Reaction products were identified based on the number of peaks in HPLC chromatograms and MS2 data.
b Mass increments of peptides in phosphate buffers of pH 7.0 are observed after treatment with β-propiolactone.
c Data are the mean ± S.D.; n = 3.
d The alanine residue is not modified. However, two reaction products were found in which one of the threonine residues was slightly modified by β-propiolactone at a pH of 9.0.
e No reaction products of β-propiolactone were detected.