@article {4314,
	title = {Equilibrium unfolding of proteins monitored by electrospray ionization mass spectrometry: Distinguishing two-state from multi-state transitions},
	journal = {Rapid Communications in Mass Spectrometry},
	volume = {12},
	number = {8},
	year = {1998},
	note = {ISI Document Delivery No.: ZJ143Times Cited: 79Cited Reference Count: 59},
	pages = {435-442},
	type = {Article},
	abstract = {The acetic acid-induced unfolding of cytochrome c (cyt c) and apomyoglobin (aMb) are studied under equilibrium conditions by electrospray ionization (ESI) mass spectrometry (MS), The folding states of the proteins in solution are monitored by the charge state distributions that they produce during ESI, A tightly folded protein shows lower charge states than the same protein in an unfolded conformation. The ESI-MS data presented in this study show that during the denaturation of cyt c, only two distinct charge state distributions are observed. These can be attributed to the native and to the acid-unfolded conformation, respectively. In the transition region where the folded and the unfolded conformation are both present in solution, these two distributions are observed simultaneously, thus giving rise to a bimodal ESI mass spectrum. These data reflect a highly cooperative (two state) folding behavior. In contrast, the acid-induced unfolding of aMb is accompanied by gradual shifts in the maxima of the observed charge state distribution. This indicates a non cooperative unfolding behavior involving multiple protein conformations. The observations made here suggest that ESI-MS might be a general method for assessing the cooperativity of protein unfolding transitions. This study also addresses the issue of {\textquoteright}secondary{\textquoteright} solvent effects for ESI-MS studies on the acid-induced unfolding of proteins. These effects influence the ESI charge state distribution without being related to conformational changes of the protein in solution and could potentially complicate the interpretation of ESI mass spectra, Data obtained for bovine pancreatic trypsin inhibitor and ubiquitin indicate that secondary solvent effects influence the observed charge state distributions only to a very minor extent between pH 8.5 and 2.5. (C) 1998 John Wiley \& Sons, Ltd.},
	keywords = {CONFORMATIONAL-CHANGES, CYTOCHROME-C, FERRICYTOCHROME-C, FOLDING, HYDROGEN-DEUTERIUM EXCHANGE, INTERMEDIATE, MOLECULAR-BASIS, MOLTEN GLOBULE, NMR-SPECTROSCOPY, POSITIVE-ION, STRUCTURAL CHARACTERIZATION},
	isbn = {0951-4198},
	url = {<Go to ISI>://000073183800005},
	author = {Konermann, L. and Douglas, D. J.}
}
@article {4029,
	title = {Acid-induced unfolding of cytochrome c at different methanol concentrations: Electrospray ionization mass spectrometry specifically monitors changes in the tertiary structure},
	journal = {Biochemistry},
	volume = {36},
	number = {40},
	year = {1997},
	note = {ISI Document Delivery No.: YA264Times Cited: 132Cited Reference Count: 51},
	month = {Oct},
	pages = {12296-12302},
	type = {Article},
	abstract = {The acid-induced denaturation of ferricytochrome c (cyt c) was examined in aqueous solutions containing different concentrations of methanol by electrospray ionization mass spectrometry (ESI MS) and optical spectroscopy. Circular dichroism, fluorescence, and absorption spectroscopy show that at a low concentration of methanol (3\%) a decrease in pH induces a cooperative unfolding transition at around pH 2.6 that is accompanied by a breakdown of the native secondary and tertiary structure of the protein. In 50\% methanol the breakdown of the tertiary structure occurs at around pH 4.0, whereas the alpha-helical content remains largely intact over the whole pH range studied. In ESI MS different protein conformations in solution are monitored by the different charge state distributions they generate during ESI. The ESI mass spectra recorded at near-neutral pH for both methanol concentrations are very similar and show a maximum at (cyt c + 8H(+))8(+). Despite the different conformations of the protein in solution, the acid-denatured states for the two methanol concentrations also show very similar mass spectra with a maximum at (cyt c + 17H(+))17(+). This indicates that the charge state distribution generated during EST is not sensitive to the differences in the secondary structure of the denatured protein. The observed transition from low to high charge states is due to the breakdown of the tertiary structure in both cases. These findings suggest that ESI MS might be a general method to selectively monitor changes in the tertiary structure of proteins.},
	keywords = {ALPHA-HELIX, BETA-LACTOGLOBULIN, CIRCULAR-DICHROISM, DENATURED, FERRICYTOCHROME-C, HEME, PARTIALLY FOLDED STATE, PROBING CONFORMATIONAL-CHANGES, PROTEIN, STATE, TRIFLUOROETHANOL},
	isbn = {0006-2960},
	url = {<Go to ISI>://A1997YA26400034},
	author = {Konermann, L. and Douglas, D. J.}
}
@article {4028,
	title = {Cytochrome c folding kinetics studied by time-resolved electrospray ionization mass spectrometry},
	journal = {Biochemistry},
	volume = {36},
	number = {18},
	year = {1997},
	note = {ISI Document Delivery No.: WY063Times Cited: 82Cited Reference Count: 46},
	month = {May},
	pages = {5554-5559},
	type = {Article},
	abstract = {A new method for studying the folding kinetics of proteins is described. The method combines a continuous flow mixing technique with an electrospray mass spectrometer. Different protein conformations in solution are detected by the different charge states they produce during electrospray ionization. Unfolded proteins generally have more accessible protonation sites and give higher charge states than native proteins. The method is applied to study the refolding of acid-denatured cytochrome c. Global data analysis is used to obtain the exponential lifetimes which are associated with the refolding process. The kinetics can be described by two lifetimes of 0.17 +/- 0.02 and 8.1 +/- 0.9 s which are in accordance with the results of stopped flow experiments previously described in the literature. These lifetimes are associated with roughly 90 and 10\% of the total intensity changes in the mass spectrum, respectively, and most likely reflect fast and slow refolding subpopulations of cytochrome c in solution.},
	keywords = {COMPLEX, denaturation, FERRICYTOCHROME-C, IRON BLEOMYCIN, LIGANDS, MECHANISM, PATHWAYS, PROBING CONFORMATIONAL-CHANGES, PROTEINS, SPECTRA},
	isbn = {0006-2960},
	url = {<Go to ISI>://A1997WY06300029},
	author = {Konermann, L. and Collings, B. A. and Douglas, D. J.}
}
