@article {2309,
	title = {Conformations of Gas-Phase Ions of Ubiquitin, Cytochrome c, Apomyoglobin, and beta-Lactoglobulin Produced from Two Different Solution Conformations},
	journal = {Journal of the American Society for Mass Spectrometry},
	volume = {19},
	number = {12},
	year = {2008},
	note = {ISI Document Delivery No.: 385IWTimes Cited: 2Cited Reference Count: 36Wright, P. John Zhang, Jianmin Douglas, D. J.},
	month = {Dec},
	pages = {1906-1913},
	type = {Article},
	abstract = {At low pH in solutions of 50\% methanol, proteins form expanded denatured states (the "H" state). In 90\% methanol, proteins form expanded helical denatured states with artificial alpha-helices (the "H-c" state). Gas-phase ions of ubiquitin, cytochrome c, apomyoglobin, and native and disulfide-reduced beta-lactoglobulin were formed by electrospray ionization (EST) of the proteins from the H and H-c states in solution. Both states in solution produce the same charge states in EST. The conformations of the ions were studied with cross section measurements and gas-phase H/D exchange experiments. The cross sections show that the ions retain considerable folded structure. For a given protein and given charge state, ions produced from the H and H-c states showed the same cross sections (within similar to 1\%). Ions of cytochrome c, apomyoglobin, and native and reduced beta-lactoglobulin of a given charge state showed no differences in H/D exchange level when produced from the H or H-c state. However, ubiquitin ions produced from the H-c state consistently exchange fewer (similar to 13\%) hydrogens than ions produced from the H state, suggesting that in this case the gas-phase protein ions retain some memory of their solution conformations. (J Am Soc Mass Spectrom 2008, 19, 1906-1913) (c) 2008 Published by Elsevier Inc. on behalf of American Society for Mass Spectrometry},
	keywords = {CIRCULAR-DICHROISM, COLLISION CROSS-SECTIONS, H/D EXCHANGE, HYDROGEN/DEUTERIUM EXCHANGE, IONIZATION MASS-SPECTROMETRY, MYOGLOBIN, OF-FLIGHT, PROTEIN IONS, STABILITY, SYSTEM, TRAP},
	isbn = {1044-0305},
	url = {<Go to ISI>://000261808900023},
	author = {Wright, P. J. and Zhang, J. M. and Douglas, D. J.}
}
@article {682,
	title = {H/D exchange of gas phase bradykinin ions in a linear quadrupole ion trap},
	journal = {Journal of the American Society for Mass Spectrometry},
	volume = {14},
	number = {2},
	year = {2003},
	note = {ISI Document Delivery No.: 643ZYTimes Cited: 14Cited Reference Count: 51},
	month = {Feb},
	pages = {85-94},
	type = {Article},
	abstract = {The gas phase H/D exchange reaction of bradykinin ions, as well as fragment ions of bradykinin generated through collisions in an orifice skimmer region, have been studied with a linear quadrupole ion trap (LIT) reflectron time-of-flight (rTOF) mass spectrometer system. The reaction in the trap takes only tens of seconds at a pressure of few mTorr of D2O or CD3OD. The exchange rate and hydrogen exchange level are not sensitive to the trapping q value over a broad range, provided q is not close to the stability boundary (q = 0.908). The relative rates and hydrogen exchange levels of protonated and sodiated +1 and +2 ions are similar to those observed previously by others with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer system. The doubly and triply protonated ions show multimodal isotopic distributions, suggesting the presence of several different conformations. The y fragment ions show greater exchange rates and levels than a or b ions, and when water or ammonia is lost from the fragment ions, no exchange is observed. (J Am Soc Mass Spectrom 2003, 14, 85-94) (C) 2003 American Society for Mass Spectrometry.},
	keywords = {ACTIVATED DISSOCIATION, COLLISIONAL ACTIVATION, CYTOCHROME-C, HYDROGEN-DEUTERIUM EXCHANGE, HYDROGEN/DEUTERIUM EXCHANGE, INFRARED, IONIZATION MASS-SPECTROMETRY, OF-FLIGHT SYSTEM, PEPTIDE IONS, PROTEIN IONS, RADIATIVE DISSOCIATION},
	isbn = {1044-0305},
	url = {<Go to ISI>://000180894500001},
	author = {Mao, D. M. and Douglas, D. J.}
}
@article {449,
	title = {Collision cross sections of gas phase DNA ions},
	journal = {International Journal of Mass Spectrometry},
	volume = {219},
	number = {1},
	year = {2002},
	note = {ISI Document Delivery No.: 591BVTimes Cited: 4Cited Reference Count: 27},
	month = {Aug},
	pages = {161-170},
	type = {Article},
	abstract = {Collision cross sections of negative ions of a 28-, 40- and 55-mer of single stranded DNA have been measured by an energy loss method, and compared to collision cross sections of proteins of nearly the same molecular weight-ubiquitin, cytochrome c and apomyoglobin, respectively. The oligonucleotides produce negative charge states in electrospray ionization (ESI) similar to the positive charge states produced by the proteins denatured in solution. Cross sections for deoxynucleotide ions increase with charge state in a manner similar to those of protein ions. However, for a given molecular weight and charge state, the cross sections of the oligodeoxynucleotide ions are about 22\% lower than those of the proteins. (C) 2002 Elsevier Science B.V. All rights reserved.},
	keywords = {collision cross sections, CONFORMATION, CONFORMERS, DNA ions, ELECTROSPRAY MASS-SPECTROMETRY, gas phase, MYOGLOBIN, PROTEIN IONS, SEQUENCE, VACUUM},
	isbn = {1387-3806},
	url = {<Go to ISI>://000177860600015},
	author = {Moradian, A. and Scalf, M. and Westphall, M. S. and Smith, L. M. and Douglas, D. J.}
}
@article {439,
	title = {Hydrogen/deuterium exchange of myoglobin ions in a linear quadrupole ion trap},
	journal = {Rapid Communications in Mass Spectrometry},
	volume = {16},
	number = {20},
	year = {2002},
	note = {ISI Document Delivery No.: 604ADTimes Cited: 10Cited Reference Count: 26},
	pages = {1941-1945},
	type = {Article},
	abstract = {The hydrogen/deuterium (H/D) exchange of gas-phase ions of holo- and apo-myoglobin has been studied by confining the ions in a linear quadrupole ion trap with D2O or CD3OD at a pressure of several mTorr. Apo-myoglobin ions were formed by collision-induced dissociation of holomyoglobin ions between the orifice and skimmer of the ion sampling system. The exchange takes place on a time scale of seconds. Earlier cross section measurements have shown that holomyoglobin ions can have more compact structures than apo-myoglobin. Despite this, both holomyoglobin and apo-myoglobin in charge states +8 to +14 are found to exchange nearly the same number of hydrogens (ca. 103) in 4 s. It is possible the ions fold or unfold to new conformations on the much longer time scale of the exchange experiment compared with the cross section measurements. Copyright (C) 2002 John Wiley Sons, Ltd.},
	keywords = {COLLISION CROSS-SECTIONS, CYTOCHROME-C, GAS-PHASE, HEME, HOLOMYOGLOBIN, HYDROGEN-DEUTERIUM EXCHANGE, MASS-SPECTROMETRY, OF-FLIGHT, PROTEIN IONS, STABILITY, SYSTEM},
	isbn = {0951-4198},
	url = {<Go to ISI>://000178592700007},
	author = {Mao, D. M. and Ding, C. F. and Douglas, D. J.}
}
@article {5189,
	title = {Collision-induced dissociation of bradykinin ions in the interface region of an ESI-MS},
	journal = {Journal of the American Society for Mass Spectrometry},
	volume = {12},
	number = {7},
	year = {2001},
	note = {ISI Document Delivery No.: 447HHTimes Cited: 17Cited Reference Count: 42},
	month = {Jul},
	pages = {772-779},
	type = {Article},
	abstract = {By applying different electric field strengths to the orifice-skimmer region of an electrospray ionization mass spectrometer, the rate of dissociation can be varied based on the amount of infernal energy acquired by an ion through collisions: with the curtain gas molecules. Both the Arrhenius equation and Rice-Ramsperger-Kassel (RRK) theory can be used to predict the rate of dissociation of internally excited molecules. A previously determined model for collision-induced dissociation is tested by comparison of predicted and experimentally observed orifice-skimmer potential differences for dissociation of ions. The rate of collision-induced dissociation of bradykinin ions is determined by monitoring the fragments produced in a mass spectrometer. The semi-quantitative model is found to yield effective predictions when accurate Arrhenius and RRK parameters are utilized. (C) 2001 American Society for Mass Spectrometry.},
	keywords = {ACTIVATION, CYTOCHROME-C, ELECTROSPRAY-IONIZATION, GAS-PHASE, IDENTIFICATION, INFRARED RADIATIVE DISSOCIATION, IONIZATION MASS-SPECTROMETRY, MOLECULES, PEPTIDES, PROTEIN IONS},
	isbn = {1044-0305},
	url = {<Go to ISI>://000169565500002},
	author = {Schneider, B. B. and Douglas, D. J. and Chen, D. D. Y.}
}
@article {4227,
	title = {Stability of a highly charged noncovalent complex in the gas phase: Holomyoglobin},
	journal = {Rapid Communications in Mass Spectrometry},
	volume = {12},
	number = {15},
	year = {1998},
	note = {ISI Document Delivery No.: 105GATimes Cited: 33Cited Reference Count: 56},
	pages = {1003-1010},
	type = {Article},
	abstract = {Gas phase holomyoglobin (hMb) ions in charge states +7 to +21 were formed by electrospray ionization in combination with a continuous-flow mixing apparatus. Collision cross section measurements show that the highly charged ions are somewhat unfolded in comparison to low charge states but still retain a considerable degree of folding. A new collision model is presented which calculates the relative energies transferred to complexes in tandem mass spectrometry. Tandem mass spectrometry and ion trapping experiments both show that the energies required to dissociate heme from the highly charged heme-protein complexes in the gas phase are similar to those of low charge states, previously shown in literature ion cyclotron resonance experiments to be 0.7-1.0 eV, These energies are comparable to those of the heme binding energy in solution. The results suggest that even for the highly charged hMb ions which have unfolded somewhat, the heme-protein interactions remain relatively unperturbed. (C) 1998 John Wiley \& Sons, Ltd.},
	keywords = {CONFORMATION, CYTOCHROME-C, ELECTROSPRAY-IONIZATION, ion-molecule, IONIZATION MASS-SPECTROMETRY, METMYOGLOBIN, MYOGLOBIN, PROTEIN IONS, PROTON-TRANSFER REACTIVITY, QUADRUPOLE, reaction},
	isbn = {0951-4198},
	url = {<Go to ISI>://000075063300003},
	author = {Chen, Y. L. and Campbell, J. M. and Collings, B. A. and Konermann, L. and Douglas, D. J.}
}
@article {3932,
	title = {Collision cross sections of myoglobin and cytochrome c ions with Ne, Ar, and Kr},
	journal = {Journal of the American Society for Mass Spectrometry},
	volume = {8},
	number = {7},
	year = {1997},
	note = {ISI Document Delivery No.: XG350Times Cited: 78Cited Reference Count: 27},
	month = {Jul},
	pages = {681-687},
	type = {Article},
	abstract = {The energy losses of ions of myoglobin and cytochrome c in collisions with Ne, Ar, and Kr have been measured with a triple quadrupole mass spectrometer system. The results have been interpreted with drag coefficients, suitable for the case of an object moving through a low density gas, to give collision cross sections or, equivalently, projection areas. For a given charge state, these cross sections with Ne, Ar, and Kr are nearly identical. No evidence is found for substantial contributions to the cross section from ion-induced dipole forces. Comparisons of cross sections obtained with different gases and comparisons to literature cross sections measured by ion mobility suggest that a {\textquoteright}{\textquoteright}diffuse{\textquoteright}{\textquoteright} scattering model,suitable for collisions with a rough surface, gives the best description of collisions between protein ions and neutrals. (C) 1997 American Society for Mass Spectrometry.},
	keywords = {GAS-PHASE, PROTEIN IONS},
	isbn = {1044-0305},
	url = {<Go to ISI>://A1997XG35000001},
	author = {Chen, Y. L. and Collings, B. A. and Douglas, D. J.}
}
@article {4006,
	title = {Dissociation of heme from myoglobin and cytochrome b(5): Comparison of behavior in solution and the gas phase},
	journal = {Biochemistry},
	volume = {36},
	number = {5},
	year = {1997},
	note = {ISI Document Delivery No.: WG072Times Cited: 79Cited Reference Count: 6144th ASMS Conference on Mass Spectrometry and Allied TopicsMAY 12-16, 1996PORTLAND, ORASMS},
	month = {Feb},
	pages = {1018-1025},
	type = {Proceedings Paper},
	abstract = {The relationship of the structure of a protein in solution to the structure of a gas-phase protein ion and the manner in which gas-phase protein ions bind small molecules noncovalently are topics of current debate. To address these issues, the stability of heme binding to wild-type and variant forms of apomyoglobin and apocytochrome bs has been studied in the gas phase by electrospray mass spectrometry (ES-MS) and compared with the stability of heme binding to the same proteins in solution. The voltage required to dissociate ions of the heme-protein complexes in the orifice-skimmer region of an electrospray mass spectrometer, a measure of the complex stability, is found to be correlated with the activation energy for dissociation of the complexes in solution across a series of proteins in which the number of hydrogen bonds between the heme propionate groups and surface residues is systematically reduced. However, variants in which the hydrogen bonds to the proximal histidine have been removed are destabilized in solution but stabilized in the gas-phase ions. These results suggest that on the millisecond time scale of the ES-MS experiment, the gas-phase protein ion may retain much of the structure of the protein in solution, at least for those residues surrounding the heme group. Furthermore, the ability of ES-MS to detect relatively subtle differences in protein-small molecule complex stability demonstrated in this work suggests that this technique may be a convenient, sensitive, and generally useful strategy for physical characterization of such complexes.},
	keywords = {ATMOSPHERIC-PRESSURE, CONFORMATION, ELECTROSPRAY MASS-SPECTROMETRY, FEATURES, IONIZATION, LARGE MOLECULES, NONCOVALENT INTERACTIONS, PROTEIN IONS, REORIENTATION, STABILITY},
	isbn = {0006-2960},
	url = {<Go to ISI>://A1997WG07200006},
	author = {Hunter, C. L. and Mauk, A. G. and Douglas, D. J.}
}
