Acidic dissociation constants of thiols

Danehy, James P.; Parameswaran, K. N.

doi:10.1021/je60038a025

Cited by 112 publications

(64 citation statements)

References 14 publications

(16 reference statements)

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“…Due to the paucity of the pK a data for the above leaving groups, one can use instead the pK a values of their nonacylated parent compounds for comparison of the properties of these leaving group. The parent compound for PI, glycerol, has a pK a of 14.2 (51); the parent compound for DPsPI, thioglycerol, has a pK a of 9.51 (52); and the pK a of p-nitrophenol is 7.14. The observed rates of the phosphorothiolate cleavage are the result of two partially compensating effects: (i) the presence of sulfur on the leaving group reduces stabilization of the transition state by the general acid (presumably a 10 5 -fold effect) due to a loss of hydrogen bonding to the leaving group; but (ii) the lower pK a of the thiol group allows more negative charge to be developed on the sulfur atom and, hence, stabilizes the transition state.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis^,

et al. 1998

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The mechanism of phosphatidylinositol-specific phospholipase C (PI-PLC) has been suggested to resemble that of ribonuclease A. The goal of this work is to rigorously evaluate the mechanism of PI-PLC from Bacillus thuringiensis by examining the functional and structural roles of His-32 and His-82, along with the two nearby residues Asp-274 and Asp-33 (which form a hydrogen bond with His-32 and His-82, respectively), using site-directed mutagenesis. In all, twelve mutants were constructed, which, except D274E, showed little structural perturbation on the basis of 1D NMR and 2D NOESY analyses. The H32A, H32N, H32Q, H82A, H82N, H82Q, H82D, and D274A mutants showed a 10 4 -10 5 -fold decrease in specific activity toward phosphatidylinositol; the D274N, D33A, and D33N mutants retained 0.1-1% activity, whereas the D274E mutant retained 13% activity. Steady-state kinetic analysis of mutants using (2R)-1,2-dipalmitoyloxypropane-3-(thiophospho-1D-myo-inositol) (DPsPI) as a substrate generally agreed well with the specific activity toward phosphatidylinositol. The results suggest a mechanism in which His-32 functions as a general base to abstract the proton from 2-OH and facilitates the attack of the deprotonated 2-oxygen on the phosphorus atom. This general base function is augmented by the carboxylate group of Asp-274 which forms a diad with His-32. The H82A and D33A mutants showed an unusually high activity with substrates featuring low pK a leaving groups, such as DPsPI and p-nitrophenyl inositol phosphate (NPIPs). These results suggest that His-82 functions as the general acid with assistance from Asp-33, facilitating the departure of the leaving group by protonation of the glycerol O3 oxygen. The Brønsted coefficients obtained for the WT and the D33N mutant indicate a high degree of proton transfer to the leaving group and further underscore the "helper" function of Asp-33. The complete mechanism also includes activation of the phosphate group toward nucleophilic attack by a hydrogen bond between Arg-69 and a nonbridging oxygen atom. The overall mechanism can be described as "complex" general acid-general base since three elements are required for efficient catalysis.Phosphatidylinositol-specific phospholipase C (PI-PLC) 1 plays a key role in receptor-mediated transformations of inositol phospholipids (1-4). The products of mammalian PI-PLC play important biological roles because they serve as a source of intracellular signaling molecules, diacylglycerol and inositol 1,4,5-trisphosphate. Diacylglycerol activates protein kinase C (5), and inositol 1,4,5-trisphosphate is involved in releasing intracellular calcium stores (6). The released calcium then activates many types of cellular processes. Glycosylphosphatidylinositol-specific phospholipase C, a subclass of PI-PLC, cleaves the spacer arm of glycosylphosphatidylinositol-anchored proteins to release extracellular enzymatic activities of these proteins (7). As shown in Figure 1, the reaction of bacterial PI-PLC consists of two steps: fast cleavage of PI int...

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Section: Discussionmentioning

confidence: 99%

Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis^,

et al. 1998

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“…18 Existing methods for thiol pKa determination include potentiometry, UV-vis, NMR, and ITC. [19][20][21][22][23][24][25] …”

Section: Introduction To Thiolsmentioning

confidence: 99%

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration

Suwandaratne

Siriwardana

et al. 2016

Anal. Chem.

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“…9 Another factor that can be crucial for the above differ ence is the low solubilities of thiolates 7 and 8 in THF under the conditions of the synthesis. This assumption is confirmed by X ray powder diffraction data for the gold thiolates under discussion.…”

Section: Methodsmentioning

confidence: 99%

“…We studied a reaction of complex 5 with tetramethyl thiuram disulfide (9). Earlier, 10 we have found that tetra alkylthiuram disulfides add to organic derivatives of gold(I), yielding gold(III) dimethyldithiocarbamates.…”

Section: Methodsmentioning

confidence: 99%

A complex of gold(I) benzenethiolate with isocyanide: synthesis and crystal and molecular structures

et al. 2010

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Acidic dissociation constants of thiols

Abstract: The acidic dissociation constants of a number of thiols have been determined and collated with those already recorded in the literature.

Cited by 112 publications

References 14 publications

Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis^,

Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis^,

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration

A complex of gold(I) benzenethiolate with isocyanide: synthesis and crystal and molecular structures

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Acidic dissociation constants of thiols

Abstract: The acidic dissociation constants of a number of thiols have been determined and collated with those already recorded in the literature.

Cited by 112 publications

References 14 publications

Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis,

Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis,

Evaluation of Thiol Raman Activities and pKa Values Using Internally Referenced Raman-Based pH Titration

A complex of gold(I) benzenethiolate with isocyanide: synthesis and crystal and molecular structures

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Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis^,

Mechanism of Phosphatidylinositol-Specific Phospholipase C: A Unified View of the Mechanism of Catalysis^,

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration