@article {828,
	title = {A one-pot synthesis and X-ray crystallographic and computational analyses of methyl-2,4-dimethoxysalicylate - a potential anti-tumour agent},
	journal = {Canadian Journal of Chemistry-Revue Canadienne De Chimie},
	volume = {82},
	number = {7},
	year = {2004},
	note = {ISI Document Delivery No.: 861XBTimes Cited: 5Cited Reference Count: 34},
	month = {Jul},
	pages = {1179-1185},
	type = {Article},
	abstract = {The thermal decarboxylation of 2-methoxycarbonyl-5-(4{\textquoteright}-nitrophen-oxy)tetrazole (1a) with the electron-rich, aromatic compounds (anisole, N,N-dimethylaniline, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene), neat or in polar solvents (DMSO, DMF, and CH3CN), is investigated. The solid phase thermal decomposition of a mixture of 1a, 1,3,5-trimethoxybenzene, and a Lewis acid (AlCl3) produces methyl-2,4-dimethoxysalicylate (8) in good yield, instead of the expected 2,4,6-trimethoxybenzoic acid. The X-ray structure of 8 shows intramolecular hydrogen bonds between the carbonyl oxygen and hydrogens of Me and OH groups. A measured pK(a) value of 6.8 compares well with a value of 6.4 estimated using the [C=O...H...O] hydrogen bond distances.},
	keywords = {2{\textquoteright}, 6{\textquoteright}-DIMETHOXYFLAVONE, ACID, anti-tumor, computational analysis, hydrogen bonds, HYDROGEN-BOND DATA, novel synthesis, PK(A), TETRAZOLES, X-ray structure},
	isbn = {0008-4042},
	url = {<Go to ISI>://000224450800007},
	author = {Dabbagh, H. A. and Noroozi-Pesyan, N. and Patrick, B. O. and James, Brian R.}
}
@article {713,
	title = {Characterizing the pH-dependent stability and catalytic mechanism of the family 11 xylanase from the alkalophilic Bacillus agaradhaerens},
	journal = {Carbohydrate Research},
	volume = {338},
	number = {5},
	year = {2003},
	note = {ISI Document Delivery No.: 645XBTimes Cited: 6Cited Reference Count: 38},
	month = {Feb},
	pages = {415-421},
	type = {Article},
	abstract = {The xylanase, BadX, from the alkalophilic Bacillus agaradhaerens was cloned, expressed and studied in comparison to a related family 11 xylanase, BcX, from B. circulans. Despite the alkaline versus neutral conditions under which these bacteria grow, BadX and BcX both exhibit optimal activity near pH 5.6 using the substrate omicron-nitrophenyl beta-xylobioside. Analysis of the bell-shaped activity profile of BadX yielded apparent pK(a) values of 4.2 and 7.1, assignable to its nucleophile Glu94 and general acid Glu184, respectively. In addition to having an similar to 10-fold higher k(cat)/K-m value with this substrate at pH 6 and 40 degreesC, BadX has significantly higher thermal stability than BcX under neutral and alkaline conditions. This enhanced stability, rather than a shift in its pH-optimum, may allow BadX to hydrolyze xylan under conditions of elevated temperature and pH. (C) 2003 Elsevier Science Ltd. All rights reserved.},
	keywords = {bacillus xylanase, CIRCULANS XYLANASE, CLASSIFICATION, electrostatic, extremophile, glycosidase, GLYCOSYL-ENZYME INTERMEDIATE, HYDROLASES, interactions, NMR ASSIGNMENTS, pH-dependent mechanism, PK(A), PROTEIN, STABILITY, THERMOSTABILITY},
	isbn = {0008-6215},
	url = {<Go to ISI>://000181004800004},
	author = {Poon, D. K. Y. and Webster, P. and Withers, S. G. and McIntosh, L. P.}
}
@article {5098,
	title = {Dissecting the electrostatic interactions and pH-dependent activity of a family 11 glycosidase},
	journal = {Biochemistry},
	volume = {40},
	number = {34},
	year = {2001},
	note = {ISI Document Delivery No.: 466CYTimes Cited: 56Cited Reference Count: 50},
	month = {Aug},
	pages = {10115-10139},
	type = {Article},
	abstract = {Previous studies of the low molecular mass family 11 xylanase from Bacillus circulans show that the ionization state of the nucleophile (GIu78, pK(a) 4.6) and the acid/base catalyst (Glu 172, pK(a) 6.7) gives rise to its pH-dependent activity profile. Inspection of the crystal structure of BCX reveals that Glu78 and Glu172 are in very similar environments and are surrounded by several chemically equivalent and highly conserved active site residues. Hence, there are no obvious reasons why their apparent pKa values are different. To address this question, a mutagenic approach was implemented to determine what features establish the pKa values (measured directly by C-13 NMR and indirectly by pH-dependent activity profiles) of these two catalytic carboxylic acids. Analysis of several BCX variants indicates that the ionized form of Glu78 is preferentially stabilized over that of Glu 172 in part by stronger hydrogen bonds contributed by two well-ordered residues, namely, Tyr69 and Gln127. In addition, theoretical pKa calculations show that Glu78 has a lower pKa value than Glu 172 due to a smaller desolvation energy and more favorable background interactions with permanent partial charges and ionizable groups within the protein. The pKa value of Glu172 is in turn elevated due to electrostatic repulsion from the negatively charged glutamate at position 78. The results also indicate that all of the conserved active site residues act concertedly in establishing the pKa values of Glu78 and Glu 172, with no particular residue being singly more important than any of the others. In general, residues that contribute positive charges and hydrogen bonds serve to lower the pKa values of Glu78 and Glu172. The degree to which a hydrogen bond lowers a pKa value is largely dependent on the length of the hydrogen bond (shorter bonds lower pKa values more) and the chemical nature of the donor (COOH > OH > CONH2). In contrast, neighboring carboxyl groups can either lower or raise the pKa values of the catalytic glutamic acids depending upon the electrostatic linkage of the ionization constants of the residues involved in the interaction. While the pH optimum of BCX can be shifted from -1.1 to +0.6 pH units by mutating neighboring residues within the active site, activity is usually compromised due to the loss of important ground and/or transition state interactions. These results suggest that the pH optima of an enzyme might be best engineered by making strategic amino acid substitutions, at positions outside of the "core" active site, that electrostatically influence catalytic residues without perturbing their immediate structural environment.},
	keywords = {ASSIGNMENTS, BACILLUS-CIRCULANS XYLANASE, CATALYSIS, GLYCOSYL-ENZYME INTERMEDIATE, KINETIC-ANALYSIS, MASS-SPECTROMETRY, MECHANISMS, NMR, PK(A), PROTEIN, SITE NUCLEOPHILE, structures},
	isbn = {0006-2960},
	url = {<Go to ISI>://000170627800014},
	author = {Joshi, M. D. and Sidhu, G. and Nielsen, J. E. and Brayer, G. D. and Withers, S. G. and McIntosh, L. P.}
}
@article {4020,
	title = {Complete measurement of the pK(a) values of the carboxyl and imidazole groups in Bacillus circulans xylanase},
	journal = {Protein Science},
	volume = {6},
	number = {12},
	year = {1997},
	note = {ISI Document Delivery No.: YK912Times Cited: 44Cited Reference Count: 29},
	month = {Dec},
	pages = {2667-2670},
	type = {Article},
	abstract = {Electrostatic interactions in proteins can be dissected experimentally by determining the pK(a), values of their constituent ionizable amino acids. To complement previous studies of the glutamic acid and histidine residues in Bacillus circulans xylanase (BCX), we have used NMR methods to measure the pK(a)s of the seven aspartic acids and the C-terminus of this protein. The pK(a)s of these carboxyls are all less than the corresponding values observed with random coil polypeptides, indicating that their ionization contributes favorably to the stability of the folded enzyme. In general, the aspartic acids with the most reduced pK(a)s are those with limited exposure to the solvent and a high degree of conservation among homologous xylanases. Most dramatically, Asp 53 and Asp 101 have pK(a)s < 2 and thus remain deprotonated in native BCX under all conditions examined. Asp 83 is completely buried, forming a strong salt bridge with Arg 136. In contrast, Asp 101 is located on the surface of the protein, stabilized in the deprotonated form by an extensive network of hydrogen bonds involving an internal water molecule and the neutral side-chain and main-chain atoms of Ser 100 and Thr 145. These data provide a complete experimental database for theoretical studies of the ionization behavior of BCX under acidic conditions.},
	keywords = {aspartic acid, electrostatics, FAMILIES, NMR, NMR ASSIGNMENTS, NUCLEAR-MAGNETIC-RESONANCE, PK(A), PROTEINS, RESIDUES, SHIFTS, titration, XYLANASE},
	isbn = {0961-8368},
	url = {<Go to ISI>://A1997YK91200024},
	author = {Joshi, M. D. and Hedberg, A. and McIntosh, L. P.}
}
