@article {1483,
	title = {Coulomb effects in binding of heme in gas-phase ions of myoglobin},
	journal = {Rapid Communications in Mass Spectrometry},
	volume = {20},
	number = {2},
	year = {2006},
	note = {ISI Document Delivery No.: 003PGTimes Cited: 3Cited Reference Count: 31},
	pages = {111-117},
	type = {Article},
	abstract = {Coulomb effects in binding of heme in gas-phase holomyoglobin ions are studied. Positive and negative ions are formed from solution myoglobin with Fe2+ (ferromyoglobin) and Fe3+ (ferrimyoglobin). The energy that must be added to the resulting holomyoglobin ions to cause heme loss has been measured by triple-quadrupole tandem mass spectrometry. With negative ions, neutral heme is lost regardless of the charge state of Fe in solution. It is likely that the Fe3+ is reduced to Fe2+ in the negative electrospray process. With positive ions, predominantly neutral heme loss is observed with ions formed from ferromyoglobin in solution, and positive heme loss with ions formed from ferrimyoglobin in solution. The energies required to induce neutral heme loss are similar for positive and negative ions. The energies required to induce charged heme loss from positive holomyoglobin ions are significantly less. Coulomb repulsion between the charged heme and charged protein appears to lower the barrier for heme loss. These results are consistent with a simple model potential with a long-range Coulomb repulsion and short-range attraction between the heme and protein. Copyright (c) 2005 John Wiley \& Sons, Ltd.},
	keywords = {B(5), COLLISION CROSS-SECTIONS, CYTOCHROME, DISSOCIATION, ELECTROSTATIC INTERACTIONS, GLOBIN COMPLEXES, HOLOMYOGLOBIN, IONIZATION-MASS-SPECTROMETRY, PROTEINS, STABILITY, ZN-MYOGLOBIN},
	isbn = {0951-4198},
	url = {<Go to ISI>://000234693500006},
	author = {Mark, K. J. and Douglas, D. J.}
}
@article {4703,
	title = {Electrostatically mediated interactions between cationic lipid-DNA particles and an anionic surface},
	journal = {Archives of Biochemistry and Biophysics},
	volume = {366},
	number = {1},
	year = {1999},
	note = {ISI Document Delivery No.: 202JKTimes Cited: 7Cited Reference Count: 29},
	month = {Jun},
	pages = {31-39},
	type = {Article},
	abstract = {In an effort to model the interaction of lipid-based DNA delivery systems with anionic surfaces, such as a cell membrane, we have utilized microelectrophoresis to characterize how electrokinetic measurements can provide information on surface charge and binding characteristics. We have established that cationic lipids, specifically N-N-dioleoyl-N,N-dimethylammonium chloride (DODAC), incorporated into liposomes prepared with I,2-dioleoyl-i-glycero-3-phosphoethanolamine (DOPE) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) at 50 mol\%, change the inherent electrophoretic mobility of anionic latex polystyrene beads. Self-assembling lipid-DNA particles (LDPs), prepared at various cationic lipid to negative DNA phosphate charge ratios, effected no changes in bead mobility when the LDP charge ratio (+/-) was equal to or less than 1. Increasing the LDP concentration in a solution of 0.1\% (w/v) anionic beads resulted in a charge reversal effect when a net charge of LDP to total bead charge ratio (+/-) of 1:1 was observed. LDP formulations, utilizing either DOPE or DOPC, showed similar titration profiles with a charge reversal observed at a 1:1 net LDP to bead charge ratio (+/-). It was confirmed through centrifugation studies that the DNA in the LDP was associated with the anionic latex beads through electrostatic interactions. LDP binding, rather than the binding of dissociated cationic lipids, resulted in the observed electrophoretic mobility changes of the anionic latex beads. (C) 1999 Academic Press.},
	keywords = {BILAYERS, CELLS, ELECTROSTATIC INTERACTIONS, FUSION, GENE-TRANSFER, lipid-DNA particles, lipoplex, LIPOSOMES, microelectrophoresis, PHOSPHATIDYLETHANOLAMINE, PLASMID DNA, VESICLES},
	isbn = {0003-9861},
	url = {<Go to ISI>://000080648400005},
	author = {Wong, F. M. P. and Bally, M. B. and Brooks, D. E.}
}
@article {3762,
	title = {The pK(a) of the general acid/base carboxyl group of a glycosidase cycles during catalysis: A C-13-NMR study of Bacillus circuluns xylanase},
	journal = {Biochemistry},
	volume = {35},
	number = {31},
	year = {1996},
	note = {ISI Document Delivery No.: VB211Times Cited: 149Cited Reference Count: 43},
	month = {Aug},
	pages = {9958-9966},
	type = {Article},
	abstract = {The 20 kDa xylanase from Bacillus circulans carries out hydrolysis of xylan via a two-step mechanism involving a covalent glycosyl-enzyme intermediate. In this double-displacement reaction, Glu78 functions as a nucleophile to form the intermediate, while Glu172 acts as a general acid catalyst during glycosylation, protonating the departing aglycone, and then as a general base during deglycosylation, deprotonating the attacking water, The dual role of Glu172 places specific demands upon its ionization states and hence pK(a) values. C-13-NMR titrations of xylanase, labeled with [delta-C-13]glutamic acid, have revealed pK(a) values of 4.6 and 6.7 for Glu78 and Glu172, respectively. These agree well with the apparent pK(a) values obtained from a study of the pH dependence of k(cat)/K-m and demonstrate that, at the enzyme{\textquoteright}s pH optimum of 5.7, the nucleophile Glu78 is deprotonated and the general acid Glu172 initially protonated. Remarkably, the pK(a) for Glu172 drops to 4.2 in a trapped covalent glycosyl-enzyme intermediate, formed by reaction with 2{\textquoteright},4{\textquoteright}-dinitrophenyl 2-deoxy-2-fluoro-beta-xylobioside [Miao et al. (1994) Biochemistry 33, 7027-7032], A similar pK(a) is measured for Glu172 when a glutamine is present at position 78. This large decrease in pK(a) of similar to 2.5 units is consistent with the role of Glu172 as a general base catalyst in the deglycosylation step and appears to be a consequence of both reduced electrostatic repulsion due to neutralization of Glu78 and a conformational change in the protein. Such {\textquoteright}{\textquoteright}pK(a) cycling{\textquoteright}{\textquoteright} during catalysis is likely to be a common phenomenon in glycosidases.},
	keywords = {ACTIVE-SITE RESIDUES, AMINO-ACIDS, beta-glucosidase, ELECTROSTATIC INTERACTIONS, ESCHERICHIA-COLI, IDENTIFICATION, LYSOZYME, MECHANISMS, NUCLEAR-MAGNETIC-RESONANCE, PROTEINS},
	isbn = {0006-2960},
	url = {<Go to ISI>://A1996VB21100003},
	author = {McIntosh, L. P. and Hand, G. and Johnson, P. E. and Joshi, M. D. and Korner, M. and Plesniak, L. A. and Ziser, L. and Wakarchuk, W. W. and Withers, S. G.}
}
