Simplification of the robinson-biggs spectrophotometric treatment of overlapping prototropic equilibria by use of isosbestic points

O'Neal, Jeffrey S.

doi:10.1016/s0003-2670(00)85637-8

Cited by 3 publications

(1 citation statement)

References 5 publications

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“…The determination of the two ground-state p Kt values of 6-HQ, with a gap of only 4 units, was performed spectrophotometrically using the treatment recommended by O'Neal and Schulman,23 and the values were found to be 5.1 ± 0.1 (>NH+/-N) and 9.2 ± 0.1 (-OH/-O™) in quite close agreement with the values of 5.17 and 8.88 previously determined. 24 The pK" value of the hydroxyl group of 1 -methyl-6-hydroxyquinolinium ion was found to be 7.0 ± 0.1, corresponding closely to previously obtained results (7.15;25 7.1-7.226); it is noteworthy that this value is more than 2 units lower than in the parent molecule 6-HQ, which shows that the electron-withdrawing effect of the quaternated nitrogen atom increases the acidity of the hydroxyl group in the ground state.…”

Section: Methodsmentioning

confidence: 99%

Photoinduced Coupled Proton and Electron Transfers. 1. 6-Hydroxyquinoline

Bardez¹,

Chatelain²,

Larrey³

et al. 1994

J. Phys. Chem.

139

196

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Section: Methodsmentioning

confidence: 99%

Photoinduced Coupled Proton and Electron Transfers. 1. 6-Hydroxyquinoline

Bardez¹,

Chatelain²,

Larrey³

et al. 1994

J. Phys. Chem.

139

196

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Isoquinolinols and Their Hydrogenated Derivatives

Hoshino¹,

Hart²,

Umezawa³

1995

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Catalytic Mechanism of S-Ribosylhomocysteinase: Ionization State of Active-Site Residues

et al. 2006

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S-Ribosylhomocysteinase (LuxS) catalyzes the cleavage of the thioether linkage in S-ribosylhomocysteine (SRH) to produce homocysteine (Hcys) and 4,5-dihydroxy-2,3-pentanedione (DPD), the precursor of type II bacterial autoinducer (AI-2). The proposed catalytic mechanism involves two consecutive ribose carbonyl migration steps via an intramolecular redox reaction and a subsequent beta-elimination step, all catalyzed by a divalent metal ion (e.g., Fe(2+) or Co(2+)) and two general acids/bases in the active site. Absorption and EPR spectroscopic studies were performed with both wild-type and various mutant forms of LuxS under a wide range of pH conditions. The studies revealed a pK(a) of 10.4 for the metal-bound water. The pK(a) value of Cys-83 was determined to be <6 by (13)C-(1)H HSQC NMR experiments with [3-(13)C]cysteine-labeled Zn(2+)-substituted Escherichia coli LuxS. The active form of LuxS contains a metal-bound water and a thiolate ion at Cys-83, consistent with the proposed roles of the metal ion (Lewis acid) and Cys-83 (general acid/base) during catalysis. Finally, an invariant Arg-39 in the active site was demonstrated to be at least partially responsible for stabilizing the thiolate anion of Cys-83.

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Simplification of the robinson-biggs spectrophotometric treatment of overlapping prototropic equilibria by use of isosbestic points

Cited by 3 publications

References 5 publications

Photoinduced Coupled Proton and Electron Transfers. 1. 6-Hydroxyquinoline

Photoinduced Coupled Proton and Electron Transfers. 1. 6-Hydroxyquinoline

Isoquinolinols and Their Hydrogenated Derivatives

Catalytic Mechanism of S-Ribosylhomocysteinase: Ionization State of Active-Site Residues

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