Solvent isotope effects and the pH dependence of laccase activity under steady-state conditions.

Koudelka, Gerald B.; Hansen, Finn B.; Ettinger, Murray J.

doi:10.1016/s0021-9258(17)36293-2

Cited by 20 publications

(14 citation statements)

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“…The interpretation that the Cu-bound water molecule is responsible for the isotope effect, i.e., a single hydrogenic site, is also consistent with the proton inventory results fitting best to a linear equation. The magnitude of the KSIE is not large (1.55) but is comparable toKSIE values reported for Cu2+-promoted amide hydrolysis (1.6) (Groves & Chambers, 1984), the lipoprotein lipase reaction (1.70) (Quinn, 1985), the hydrolysis of pyrophosphate by inorganic pyrophosphatase (1.9) (Konsowitz & Cooperman, 1976), and the reaction catalyzed by the multicopper oxidase lacease (2.1) (Koudelka & Ettinger, 1985). The KSIE on kcat can be related to the ratio of the fractionation factors for the reactant state [0(RS)] and the transition state [0(TS)] (Kresge, 1977).…”

Section: Discussionsupporting

confidence: 78%

“…A similar mechanism may obtain for Cu2+-and Zn2+-catalyzed amide hydrolysis by a model complex (Groves & Chambers, 1984). Also relevant is the pH dependence and kinetic solvent isotope effect observed for lacease turnover (Koudelka & Ettinger, 1985). As noted for GO, the binding of a water molecule to the type 2 (nonblue) Cu(II) in lacease has been detected by using 170 ESR (Deinum & Vánngárd, 1975).…”

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confidence: 55%

“…As noted for GO, the binding of a water molecule to the type 2 (nonblue) Cu(II) in lacease has been detected by using 170 ESR (Deinum & Vánngárd, 1975). The reductant independent pH-rate profile (descending) for lacease exhibits (in H20) a pKí2 = 5.91, a pKa2 in D20 of 6.17, and a KSIE of 2.12 (Koudelka & Ettinger, 1985). These values could be attributed to the Cu2+-H20 species in lacease acting as a proton donor during turnover.…”

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confidence: 86%

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Solvent and solvent proton dependent steps in the galactose oxidase reaction

Driscoll

Kosman²

1987

Biochemistry

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Solvent and solvent proton dependent steps involved in the mechanism of the enzyme galactose oxidase have been examined. The deuterium kinetic solvent isotope effect (KSIE) on the velocity of the galactose oxidase catalyzed oxidation of methyl beta-galactopyranoside by O2 was measured. Examination of the thermodynamic activation parameters for the reaction indicated that the isotope effect was attributable to a slightly less favorable delta H value, consistent with a KSIE on proton transfer. A detailed kinetic analysis was performed, examining the effect of D2O on the rate of reaction over the pH range 4.8-8.0. Both pL-rate profiles exhibited bell-shaped curves. Substitution of D2O as solvent shifted the pKes values for the enzymic central complex: pKes1 from 6.30 to 6.80 and pKes2 from 7.16 to 7.35. Analysis of the observed shifts in dissociation constants was performed with regard to potential hydrogenic sites. pKes1 can be attributed to a histidine imidazole, while pKes2 is tentatively assigned to a Cu2+-bound water molecule. A proton inventory was performed (KSIE = +1.55); the plot of kcat vs. mole fraction D2O was linear, indicating the existence of a single solvent-derived proton involved in a galactose oxidase rate-determining step (or steps). The pH dependence of CN- inhibition was also examined. The Ki-pH profile indicated that a group ionization, with pKa = 7.17, modulated CN- inhibition; Ki was at a minimum when this group was in the protonated state. The inhibition profile followed the alkaline limit of the pH-rate profile for the enzymic reaction, suggesting that the group displaced by CN- was also deprotonating above pH 7.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Discussionsupporting

confidence: 78%

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confidence: 55%

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confidence: 86%

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Solvent and solvent proton dependent steps in the galactose oxidase reaction

Driscoll

Kosman²

1987

Biochemistry

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“…Because butyric acid produced by the hydrolytic activity of esterase partially dissociates in aqueous solution, the initial pH of the solution decreases. It is known , that the overall rate of reactions biocatalyzed by laccase (the second enzyme in the system) strongly depends on pH, being very slow at pH values above 8.1. Therefore, change in pH, caused by the hydrolytic reaction biocatalyzed by esterase, activates the reaction of laccase (0.5 U·mL –1 equal to 3.78 × 10 –4 mM based on the average molecular weight of 66 kDa for fungal laccases − ), which catalyzes the oxidation of 1 mM ferrocyanide in the presence of oxygen.…”

Section: Methodsmentioning

confidence: 99%

“…Because butyric acid produced by the hydrolytic activity of esterase partially dissociates in aqueous solution the initial pH of the solution decreases. It is known 52,53 that overall rate of reactions biocatalyzed by laccase (the second enzyme in the system) strongly depends on pH, being very slow at pH values above 8.1.…”

Section: Composition and Mapping Of The Or Gate With Double Sigmoid F...mentioning

confidence: 99%

Enzyme-Based Logic: OR Gate with Double-Sigmoid Filter Response

et al. 2012

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The first realization of a biomolecular OR gate function with double-sigmoid response (sigmoid in both inputs) is reported. Two chemical inputs activate the enzymatic gate processes resulting in the output signal: chromogen oxidation, which occurs when either one of the inputs or both are present (corresponding to the OR binary function), and can be optically detected.High-quality gate functioning in handling of sources of noise is enabled by "filtering" involving pH control with an added buffer. The resulting gate response is sigmoid in both inputs when proper system parameters are chosen, and the gate properties are theoretically analyzed within a model devised to evaluate its noise-handling properties.

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Copper Proteins: Oxidases

Stoj¹,

Kosman²

2005

Encyclopedia of Inorganic Chemistry

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Oxidases are enzymes that use dioxygen as the electron acceptor in oxido‐reduction reactions. Many members of this enzyme class (EC 1.) rely on the Cu 1+ /Cu 2+ redox cycle of copper prosthetic group(s) in their catalysis of the electron transfer from reducing substrate to O 2 . Those copper oxidases that catalyze the four‐electron reduction of O 2 to 2H 2 O are known as multicopper oxidases (MCO) because each member of this group contains at least four copper atoms of three distinct electronic and spectral types. These three types are: type 1 or ‘blue’ Cu(II), so‐called because of its distinguishing strong absorbance at ∼600 nm; type 2 Cu(II), comparable in electronic structure to that found in square‐planar copper complexes; and type 3 Cu(II), a Cu(II)Cu(II) pair bridged by O(H) and thus diamagnetic. With four 1e − metal redox sites, MCOs are the all‐copper equivalent of the copper‐heme respiratory terminal oxidases. However, MCOs are true oxidases in that all members can use as electron acceptors common (di)phenolic, and aromatic (di)amine substrates, for example, hydroquinone, ascorbic acid, and phenylenediamine. The laccases and ascorbate oxidase are examples of these MCOs (EC 1.10.3). Members of a separate MCO class (EC 1.16.3) also use lower valent metal ions as substrates, for example, Fe 2+ , Cu 1+ , and/or Mn 2+ . These are thereby designated metallo‐oxidases; the most widely studied activity of this class has been towards Fe 2+ giving rise to the common enzyme name, ferroxidase. The typical MCO structure consists of three ‘cuprodoxin’ domains, a Greek‐key beta‐fold that characterizes a family of mononuclear copper electron‐transfer factors. Among MCOs are both soluble and type 1 membrane proteins. Functionally, MCOs are known to play essential roles in biodegradation and transformation, cell redox balance, and metal metabolism. This article summarizes current knowledge of this class of copper oxidase enzymes.

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Solvent isotope effects and the pH dependence of laccase activity under steady-state conditions.

Cited by 20 publications

References 25 publications

Solvent and solvent proton dependent steps in the galactose oxidase reaction

Solvent and solvent proton dependent steps in the galactose oxidase reaction

Enzyme-Based Logic: OR Gate with Double-Sigmoid Filter Response

Copper Proteins: Oxidases

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