* To whom correspondence should be addressed.
Received February 24, 2012; Revision received March 11, 2012
The number of protons available for hydrogen–deuterium exchange was predicted for ten globular proteins using a method described elsewhere by the authors. The average number of protons replaced by deuterium was also determined by mass spectrometry of the intact proteins in their native conformations. Based on these data, we find that two models proposed earlier agree with each other in estimation of the number of protons replaced by deuterium. Using a model with a probability scale for hydrogen bond formation, we estimated a number of protons replaced by deuterium that is close to the experimental data for long-term incubation in D2O (24 h). Using a model based on estimations with a scale of the expected number of contacts in globular proteins there is better agreement with the experimental data obtained for a short period of incubation in D2O (15 min). Therefore, the former model determines weakly fluctuating parts of a protein that are in contact with solvent only for a small fraction of the time. The latter model (based on the scale of expected number of contacts) predicts either flexible parts of a protein chain exposed to interactions with solvent or disordered parts of the protein.
KEY WORDS: hydrogen–deuterium exchange, secondary structure, hydrogen bond, mass spectrometry