期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1982
卷号：79
期号：5
页码：1418-1422
DOI：10.1073/pnas.79.5.1418
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Hydrogen exchange has been studied in a single crystal of RNase A [ribonuclease (pancreatic), EC 3.1.27.5 ] in the course of a neutron structure investigation. Refinement of the occupancies of amide hydrogens provided information about the kind of isotope present in each site and also provided estimates of the errors associated with the measurement. Twenty-eight of the 120 peptide amide hydrogens were found to be at least partially protected from exchange during approximately 1 year required for crystal preparation and data collection. Most of the protected hydrogens were involved in hydrogen bonds with main-chain carbonyl groups. A contiguous region of the beta-sheet containing residues 75, 106--109, 116, and 118 had a large number of protected hydrogens, indicating its low flexibility and the lack of accessibility to solvent. Residues 11--13 from the alpha-helix near the amino terminus were protected, in good agreement with a model of cooperative unwinding of this helix, starting from the free (amino) end.
