Reversible hydration of pyruvic acid. I. Equilibrium studies

Pocker, Y.; Meany, J. E.; Nist, Bernard J.; Zadorojny, C.

doi:10.1021/j100843a015

Cited by 102 publications

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“…In an earlier study, the rate of dehydration of hydrated pyruvic acid was found to be dependent on the pyruvate ion concentration. 64 This is in sharp contrast with our finding because the rate constant is independent of pyruvate ion concentration in the 5.010 −4 -1.010 −2 M concentration range. Furthermore, according to our results the proton catalyzed step is considerably slower and the non-catalytic reaction is much faster than it was reported earlier.…”

Section: Kinetic Studies Under Acidic Conditionscontrasting

confidence: 99%

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The kinetics and mechanism of the oxidation of pyruvate ion by hypochlorous acid

et al. 2015

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The oxidation of pyruvic acid by hypochlorous acid was studied in the pH 1.0 -11.0 range. The main path in the redox process is the reaction between the pyruvate ion and HOCl. It was shown that the reaction is second order in both reactants and kHOCl = 2.14 ± 0.02M −1 s −1 (I = 1.0 M (NaClO4), T = 25.0 °C) with ∆HHOCl ≠ = 34.6 ± 1.2 kJmol −1 and ∆SHOCl ≠ = −120.3 ± 3.6 Jmol −1 K −1 for this reaction step. The relatively large negative entropy of activation is consistent with an O atom-transfer mechanism. DFT calculations support this conclusion by predicting a concerted rearrangement of the activated complex which includes the reactants and the solvent water molecule. It was also confirmed that the hydration of pyruvic acid has significant contribution to the observed kinetic features under acidic condition. The hydration reaction is a proton catalyzed process and the pseudo-first order rate constant can be interpreted by considering theprotolytic and hydration equilibria of pyruvic acid. The rate constants were determined for the non-catalytic and the proton catalyzed path: kh0 = 0.24 ± 0.01 s −1 and kh1 = 5.5 ± 0.2 M −1 s −1 .

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Section: Kinetic Studies Under Acidic Conditionscontrasting

confidence: 99%

“…[63][64][65][66] Scheme 1 shows all the possible equilibrium steps together with the corresponding equilibrium constants for the pyruvate system. 63 Scheme 1 Acid -base, keto -enol and hydration equilibria in aqueous solution of pyruvate ion.…”

Section: Kinetic Studies Under Acidic Conditionsmentioning

confidence: 99%

The kinetics and mechanism of the oxidation of pyruvate ion by hypochlorous acid

et al. 2015

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“…It is known that PA is reversibly hydrated in aqueous solution to its gem-diol and that the equilibrium is both pH-and temperature-dependent, with lower pH and lower temperature both favoring the hydrate (51,52). In aqueous solution at 298 K, ∼35% of PA exists in its keto form, with the majority existing as its gem-diol (13,45,46).…”

Section: Discussionmentioning

confidence: 99%

Photochemistry of aqueous pyruvic acid

Griffith

Carpenter

Shoemaker³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

126

289

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The study of organic chemistry in atmospheric aerosols and cloud formation is of interest in predictions of air quality and climate change. It is now known that aqueous phase chemistry is important in the formation of secondary organic aerosols. Here, the photoreactivity of pyruvic acid (PA; CH 3 COCOOH) is investigated in aqueous environments characteristic of atmospheric aerosols. PA is currently used as a proxy for α-dicarbonyls in atmospheric models and is abundant in both the gas phase and the aqueous phase (atmospheric aerosols, fog, and clouds) in the atmosphere. The photoreactivity of PA in these phases, however, is very different, thus prompting the need for a mechanistic understanding of its reactivity in different environments. Although the decarboxylation of aqueous phase PA through UV excitation has been studied for many years, its mechanism and products remain controversial. In this work, photolysis of aqueous PA is shown to produce acetoin (CH 3 CHOHCOCH 3 ), lactic acid (CH 3 CHOHCOOH), acetic acid (CH 3 COOH), and oligomers, illustrating the progression from a three-carbon molecule to four-carbon and even six-carbon molecules through direct photolysis. These products are detected using vibrational and electronic spectroscopy, NMR, and MS, and a reaction mechanism is presented accounting for all products detected. The relevance of sunlight-initiated PA chemistry in aqueous environments is then discussed in the context of processes occurring on atmospheric aerosols.

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“…32,[40][41][42] However, in the active site of MR, it is possible that coordination of the metal ion could lead to dehydration of the gem-diols, yielding the corresponding keto species. 43 It is unlikely, however, that this latter possibility would result in a significant alteration of the binding affinity considering our observations with pyruvate and lactate, and benzoylformate and mandelate, mentioned above. VERSION; this is the author's final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation at the bottom of the page.…”

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confidence: 75%

Inactivation of Mandelate Racemase by 3-Hydroxypyruvate Reveals a Potential Mechanistic Link between Enzyme Superfamilies

et al. 2015

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Mandelate racemase (MR), a member of the enolase superfamily, catalyzes the Mg 2+ -dependent interconversion of the enantiomers of mandelate. Several α-keto acids are modest competitive inhibitors of MR [e.g., mesoxalate (Ki = 1.8 ± 0.3 mM) and 3-fluoropyruvate (Ki = 1.3 ± 0.1 mM)], but, surprisingly, 3-hydroxypyruvate (3-HP) is an irreversible, time-dependent inhibitor (kinact/KI = 83 ± 8 M -1 s -1 ). Protection from inactivation by the competitive inhibitor benzohydroxamate, trypsinolysis and electrospray ionization tandem mass spectrometry analyses, and X-ray crystallographic studies reveal that 3-HP undergoes Schiff-base formation with Lys 166 at the active site, followed by formation of an aldehyde/enol(ate) adduct. Such a reaction is unprecedented in the enolase superfamily and may be a relic of an activity possessed by a promiscuous progenitor enzyme. The ability of MR to form and deprotonate a Schiff-base intermediate furnishes a previously unrecognized mechanistic link to other α/β-barrel enzymes utilizing Schiff-base chemistry and is in accord with the sequence-and structure-based hypothesis that members of the metal-dependent enolase superfamily and the Schiff-baseforming N-acetylneuraminate lyase superfamily and aldolases share a common ancestor.One of the first enzyme superfamilies recognized was the enolase superfamily, 1 whose members share a common partial reaction (i.e., the metal-assisted, Brønsted-base-catalyzed abstraction of the α-proton from a carboxylate substrate to form an enolate) 2-5 and a common protein fold [i.e., a modified (α/β)8-barrel (TIM barrel) bearing the catalytic residues at the C-terminal ends of the β-strands and an N-terminal domain that caps the active site conferring substrate specificity and excluding solvent]. [6][7][8] Studies of members of the enolase superfamily have afforded important insights into enzyme evolution and developing strategies for assigning the correct functions to proteins identified in genome projects. 3,[9][10][11][12] The well-characterized NOT THE PUBLISHED VERSION; this is the author's final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation at the bottom of the page.Biochemistry, Vol 54, No. 17 (May 5, 2015): pg. 2747-2757. DOI. This article is © American Chemical Society and permission has been granted for this version to appear in e-Publications@Marquette. American Chemical Society does not grant permission for this article to be further copied/distributed or hosted elsewhere without the express permission from American Chemical Society. 3archetype of this superfamily, mandelate racemase (MR, EC 5.1.2.2) from Pseudomonas putida, catalyzes the Mg 2+ -dependent, 1,1-proton transfer reaction that interconverts the enantiomers of mandelate and has served as a useful paradigm for understanding how enzymes catalyze the rapid α-deprotonation of a carbon acid substrate with a relatively high pKa value. 13 MR utilizes a two-base mechanism with Lys 166 and His 297 abstracting the α-proton fr...

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Reversible hydration of pyruvic acid. I. Equilibrium studies

Cited by 102 publications

References 0 publications

The kinetics and mechanism of the oxidation of pyruvate ion by hypochlorous acid

The kinetics and mechanism of the oxidation of pyruvate ion by hypochlorous acid

Photochemistry of aqueous pyruvic acid

Inactivation of Mandelate Racemase by 3-Hydroxypyruvate Reveals a Potential Mechanistic Link between Enzyme Superfamilies

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