Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.2.13 (aldolase)
 3,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Amide hydrogen exchange has been measured in short segments of intact rabbit muscle aldolase at temperatures of 14-50 degrees C by the protein fragmentation/mass spectrometry method (Zhang Z, Smith DL, 1993, Protein Sci 2:522-531). Deuterium levels in some segments did not change over the temperature range of the measurements, whereas deuterium levels in other segments increased rapidly with temperature. These results demonstrate that the equilibrium constant for local unfolding, Kunf, of some segments increases with temperature in the low temperature range (14-30 degrees C) of this study. Aldolase begins to lose activity at temperatures above 40 degrees C. In the 40-50 degrees C temperature range, Kunf is greater than 10(-4) in some regions and less than 10(-6) in other regions. This wide range of regional stability in the temperature range where aldolase begins to denature is interpreted in terms of cooperative unfolding/folding domains. Regions of highest stability were located along the hydrophobic subunit binding surface. It is proposed that hydrogen exchange might be used to identify unfolding domains in multidomain proteins whose thermodynamic properties have been determined by differential scanning calorimetry.
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PMID:Thermal-induced unfolding domains in aldolase identified by amide hydrogen exchange and mass spectrometry. 881 61

Amide hydrogen exchange rates, determined by NMR spectroscopy, have become an important tool that is often used to investigate structure and dynamics of small proteins. Recent developments in mass spectrometry and sample handling methods make possible measurement of deuterium levels at peptide amide linkages in polypeptides. The ability to make these measurements has led to development of the protein fragmentation/mass spectrometry approach for determining amide hydrogen exchange rates in short segments of intact proteins following their incubation in D2O. Partially deuterated proteins are proteolytically fragmented into peptides whose molecular weights are determined by on-line liquid chromatography/mass spectrometry. Deuterium levels, which are determined from the molecular weights of the peptic fragments, can be used to determine amide hydrogen exchange rates. Details of the protein fragmentation/mass spectrometry approach, along with a brief review of the theory of amide hydrogen exchange, are described. The ability to detect and locate minor structural differences in proteins by the protein fragmentation/mass spectrometry approach is illustrated using oxidized and reduced cytochrome c. These results show that oxidation of iron has little effect on the N- and C-terminal regions, but significantly destabilizes the interior regions of cytochrome c. The ability to detect localized unfolding in large proteins is illustrated with aldolase that was equilibrated in acid. Despite the success achieved by NMR spectroscopy for determining amide hydrogen exchange rates, mass spectrometry is advantageous because it permits studies of large proteins, requires only picomoles of protein, and provides a direct measure of structural heterogeneity.
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PMID:Local structure and dynamics in proteins characterized by hydrogen exchange and mass spectrometry. 952 25

In contrast to the rigid structures portrayed by X-ray diffraction, proteins in solution display constant motion which leads to populations that are momentarily unfolded. To begin to understand protein dynamics, we must have experimental methods for determining rates of folding and unfolding, as well as for identifying structures of folding and unfolding intermediates. Amide hydrogen exchange has become an important tool for such measurements. When urea is used to stabilize unfolded forms of proteins, the refolding rates may become slower than the rates of isotope exchange. In such cases, the intermolecular distribution of deuterium among the entire population of molecules may become bimodal, giving rise to a bimodal distribution of isotope peaks in mass spectra of the protein or its peptic fragments. When the protein is exposed continuously to D2O, the relative intensities of the two envelopes of isotope peaks give an integrated account of populations participating in the folding/unfolding process. However, when the protein is exposed only briefly to D2O, the relative intensities of the two envelopes of isotope peaks give an instantaneous measure of the folded/unfolded populations. Application of these two labeling methods to a large protein, aldolase, is described along with a discussion of specific parameters required to optimize these experiments.
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PMID:Comparison of continuous and pulsed labeling amide hydrogen exchange/mass spectrometry for studies of protein dynamics. 1043 6