Hydrogen exchange is an interchange of hydrogen atom of a molecule (protein, nucleic acid, etc.) with that of the solvent (Englander and Kallenbach 1983). It is catalyzed by both acid (H3O+) and base (OH).
In general, the hydrogen exchange rate constants (krc) vary with temperature and pH. When log (krc) is plotted against pH, it gives rise to a v-shaped curve with a minimum around pH 3.0. In a random coil peptide, the krc of an individual amide proton (1HN) further depends on the amino acid sequence (due to the inductive and steric effects of neighboring residues). All these effects can be taken together to predict respective krc (Bai factors) of any given protein sequence (Bai et al. 1993).
In folded proteins, the observed 1HN exchange rates (kobs) are much smaller than the predicted krc, and such retardation in exchange process is expressed in terms of protection factor, P (krc/kobs), that can range from value 1 (completely unprotected) to 1010or higher for significantly protected...
- Hwang T-L, Mori S, Shaka AJ, van Zijl PCM (1997) Application of Phase-Modulated CLEAN chemical EXchange spectroscopy (CLEANEX-PM) to detect water–protein proton exchange and intermolecular NOEs. J Am Chem Soc 119:6203–6204Google Scholar
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