Table 2.
Random coil chemical shifts (ppm) of isoAsp and Snn in small model peptides in 7 M urea-d4, D2O at two pH values (2.3, 7.4)
| Peptide | Ac-Gly-Gly-IsoAsp-Gly-Gly-Gly-NH2 | Previously reported valuesc | ||||
|---|---|---|---|---|---|---|
| Amino acid | isoAsp | Snnb | isoAsp | Snn | ||
| pH | 2.3 | 7.4 | 2.3 | 7.4 | 2.3 | 2.3 |
| C | 177.0 | 179.5 | 180.0 | n.d | 177.0 | 179.5 |
| Cα | 52.3 | 54.8 | 51.8 | 51.8 | 52.3 | 52.0 |
| Cβ | 39.4 | 40.8 | 37.4 | 37.4 | 39.5 | 37.5 |
| Cɣ | 175.5 | 176.5 | n.d | n.d | 175.3 | 179.9 |
| Hα | 4.81 | 4.55 | 4.78 | 4.78 | 4.79 | 4.78 |
| Hβ2a | 2.93 | 2.83 | 3.26 | 3.27 | 2.92 | 3.26 |
| Hβ3a | 2.93 | 2.75 | 2.87 | 2.86 | 2.92 | 2.87 |
aβ2 and β3 chemical shifts are not sterochemically assigned, the lower value was tentatively assigned to Hβ3
bSmall amounts of Snn were detected (~ 35%) due to its equilibrium with isoAsp; n.d. not determined
cRandom coil chemical shifts reported earlier (Grassi et al. 2017) measured at pH 2.3 with the peptides Ac-Glu-Trp-Ser-isoAsp-Gly-Gln-Pro-Glu-Asn-NH2 and Ac-Glu-Trp-Ser-Snn-Gly-Gln-Pro-Glu-Asn-NH2