@article{oai:ir.soken.ac.jp:00004127,
 author = {桑島, 邦博 and KUWAJIMA, Kunihiro and BALDWIN, Robert L},
 issue = {1},
 journal = {Journal of Molecular Biology, Journal of Molecular Biology},
 month = {Sep},
 note = {The locations have been found of the eight most slowly exchanging peptide protons in residues 1 to 19 of ribonuclease S. The resonance lines of these eight protons are resolved by proton magnetic resonance at 360 MHz when either S-peptide (residues 1 to 19) or peptide 1-15 is bound to S-protein (residues 21 to 124). Other peptide protons have been removed by exchange in the sample preparation ([1H]S-peptide is added to deuterated S-protein in D2O), and also by exchange-out of the less protected protons in residues 1 to 19.

At pH 5·1, 0°C, there is a 100-fold difference in rates of exchange between the eight most protected protons and the less protected protons of S-peptide. The highly protected protons are protected 104-fold compared to free S-peptide. The protected protons have been identified by 1H nuclear magnetic resonance after denaturing ribonuclease S in ≥3 m-urea-d4, D2O, pH 2·3, −4°C, followed by comparing the chemical shifts of the remaining eight protons with the known -NH spectrum of the free peptide, which has been assigned from the two-dimensional homonuclear correlated spectrum and by comparison with earlier work.

The eight highly protected NH protons are localized in one segment, residues 7 to 14. All eight protons are H-bonded: those of residues 7 to 13 are H-bonded within the 3-13 α-helix and that of residue 14 is H-bonded to the β-sheet. The NH proton of residue 16, which also is H-bonded to the β-sheet, is not one of the highly protected protons. Both the N atoms of the eight NH groups and also the O atoms of their CO acceptor groups are shielded from solvent in most cases, according to the molecular area calculations of Finney (1978).},
 pages = {281--297},
 title = {Nature and locations of the most slowly exchanging peptide NH protons in residues 1 to 19 of ribonuclease S},
 volume = {169},
 year = {1983}
}