Molecular Properties and Reaction Mechanism of Multicopper Oxidases Related to Their Use in Biofuel Cells

Solomon, Edward I.; Kjaergaard, Christian H.; Heppner, David E.

doi:10.1002/9781118899076.ch8

Cited by 5 publications

(4 citation statements)

References 109 publications

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“…The type 1 Cu reduction potential ranges widely among MCOs (0.3–0.8 V − ), and that of Mnx might have been expected to be quite high. Yet, our measured value, E 0 = 0.38 V (pH 7.8), is near the low end of the range.…”

Section: Resultsmentioning

confidence: 99%

Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism

Soldatova

Tao²,

Romano

et al. 2017

J. Am. Chem. Soc.

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The bacterial protein complex Mnx contains a multicopper oxidase (MCO) MnxG that, unusually, catalyzes the two-electron oxidation of Mn(II) to MnO biomineral, via a Mn(III) intermediate. Although Mn(III)/Mn(II) and Mn(IV)/Mn(III) reduction potentials are expected to be high, we find a low reduction potential, 0.38 V (vs Normal Hydrogen Electrode, pH 7.8), for the MnxG type 1 Cu, the electron acceptor. Indeed the type 1 Cu is not reduced by Mn(II) in the absence of molecular oxygen, indicating that substrate oxidation requires an activation step. We have investigated the enzyme mechanism via electronic absorption spectroscopy, using chemometric analysis to separate enzyme-catalyzed MnO formation from MnO nanoparticle aging. The nanoparticle aging time course is characteristic of nucleation and particle growth; rates for these processes followed expected dependencies on Mn(II) concentration and temperature, but exhibited different pH optima. The enzymatic time course is sigmoidal, signaling an activation step, prior to turnover. The Mn(II) concentration and pH dependence of a preceding lag phase indicates weak Mn(II) binding. The activation step is enabled by a pK > 8.6 deprotonation, which is assigned to Mn(II)-bound HO; it induces a conformation change (consistent with a high activation energy, 106 kJ/mol) that increases Mn(II) affinity. Mnx activation is proposed to decrease the Mn(III/II) reduction potential below that of type 1 Cu(II/I) by formation of a hydroxide-bridged binuclear complex, Mn(II)(μ-OH)Mn(II), at the substrate site. Turnover is found to depend cooperatively on two Mn(II) and is enabled by a pK 7.6 double deprotonation. It is proposed that turnover produces a Mn(III)(μ-OH)Mn(III) intermediate that proceeds to the enzyme product, likely Mn(IV)(μ-O)Mn(IV) or an oligomer, which subsequently nucleates MnO nanoparticles. We conclude that Mnx exploits manganese polynuclear chemistry in order to facilitate an otherwise difficult oxidation reaction, as well as biomineralization. The mechanism of the Mn(III/IV) conversion step is elucidated in an accompanying paper .

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Section: Resultsmentioning

confidence: 99%

Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism

Soldatova

Tao²,

Romano

et al. 2017

J. Am. Chem. Soc.

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“…The reduction and protonation of molecular oxygen (dioxygen, O 2 ) to hydrogen peroxide or water is a critical component of “dioxygen activation” chemistry effected by transition metal ions, i.e., for use of O 2 as an energy source in fuel cell applications (O 2 + 4e – + 4H + → 2H 2 O) , or in oxidative chemistries including oxygen-atom transfer from O 2 to substrates (e.g., as in monooxygenases such as cytochrome P450; R–H + O 2 + 2H + + 2e – → R–OH + H 2 O), dehydrogenation (SH 2 + O 2 → S + H 2 O 2 ) or oxidase reactions (e.g., 4AH + O 2 → 4A + 2H 2 O). , As relevant to these processes, considerable insight can be obtained from copper metalloenzyme studies which perform these biologically essential functions including the use of molecular oxygen for the functionalization/incorporation of oxygen atom(s) into organic substrates, ,, the production of signaling agents, ,, or regulation of cellular energy flux through the utilization of dioxygen as a terminal electron acceptor . Nature has evolved to include a diverse repertoire of copper active site configurations containing one to four copper ions with some possessing another redox active site to facilitate dioxygen reduction chemistries in oxidase and oxygenase systems.…”

Section: Introductionmentioning

confidence: 99%

Stepwise Protonation and Electron-Transfer Reduction of a Primary Copper–Dioxygen Adduct

et al. 2013

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The protonation-reduction of a dioxygen adduct with [LCuI][B(C6F5)4], cupric superoxo complex [LCuII(O2•−)]+ (1), (L=TMG3tren(1,1,1-tris[2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl]amine)), has been investigated. Trifluoroacetic acid (HOAcF) reversibly associates with the superoxo ligand in ([LCuII(O2•−)]+) in a 1:1 adduct [LCuII(O2•−)(HOAcF)]+ (2), as characterized by UV-visible, resonance Raman (rR), nuclear magnetic resonance (NMR) and X-ray absorption (XAS) spectroscopies, along with density functional theory (DFT) calculations. Chemical studies reveal that for the binding of HOAcF with 1 to give 2, Keq = 1.2×105 M−1 (−130 °C) and ΔH° = − 6.9(7) kcal/mol, ΔS° = − 26(4) cal/mol•K). Vibrational (rR) data reveal a significant increase (29 cm−1) in νO-O (= 1149 cm−1) compared to that known for [LCuII(O2•−)]+ (1). Along with results obtained from XAS and DFT calculations, hydrogen bonding of HOAcF to a superoxo O-atom in 2 is established. NMR spectroscopy of 2 at −120 °C in 2-methyltetrahydrofuran are also consistent with 1/HOAcF = 1:1 formulation 2 and that this complex possesses a triplet (S = 1) ground state electronic configuration, as previously determined for 1. The pre-equilibrium acid association to 1 is followed by outer-sphere electron-transfer reduction of 2 by decamethylferrocene (Me10Fc) or octamethylferrocene (Me8Fc), leading to the products H2O2, the corresponding ferrocenium salt and [LCuII(OAcF)]+. Second-order rate constants for electron transfer (ket) were determined to be 1365 M−1 s−1 (Me10Fc) and 225 M−1 s−1 (Me8Fc) at −80 °C. The (bio)chemical relevance of the proton-triggered reduction of the metal-bound dioxygen-derived fragment is discussed.

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“…The RP difference value between phenolic compound and T1-Cu site augmented with pH, thus improving the conversion kinetics of substrate (Mateljak et al, 2019). On the other hand, the enzymatic reaction of phenolic contaminants is also impeded at high pH (usually, pH was greater than 6.0) because of the limitation of the intramolecular electron transfer (Solomon et al, 2015). Some reports stated that OH − was bene cial to bind with T2/T3-Cu sites in laccase, which terminated the internal-electron transfer and thus suppressed the reactivity of laccase (Xu, 1997;Wang et al, 2018).…”

Section: Tvlac-evoked Humi Cation Kinetics Of E2 With Has At Varying mentioning

confidence: 99%

Effect of Two Humic Acids on Laccase-Driven 17β-Estradiol Conversion Kinetics and Polymerization Products at Varying pH Levels

Kim

Zhu

et al. 2021

Preprint

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Estrogens with tremendous ecological risks are proverbially found in water. Laccase can drive humification of estrogens to reduce their ecotoxicity and removability, but little investigation existed in exploring the effect of humic acids (HAs) on E2 conversion kinetics and polymerization products at different pH conditions. Here, Trametes versicolor laccase (Tvlac) was capable of efficiently converting a representative estrogen, 17β-estradiol (E2) with two different HAs, and the process followed a pseudo-first-order kinetics. The velocity constants were respectively 0.048, 0.022, and 0.020 min− 1 for HA-free, peat-derived HA, and commercial HA at pH 5.0. The changing pH not only impacted E2 coupling kinetics in Tvlac-evoked humification, but altered the aromaticity and humification degrees of HAs. A total of five intermediate species including estrone (E1), E2 dimer, trimer, and tetramer, as well as E1-E2 cross-linked products were tentatively detected, in which the dominating species were E2 self-oligomers resulting from radical-centered carbon-carbon/oxygen stepwise polymerization routes. Yields of dimeric, trimeric, and tetrameric species with increased molecular sizes were the highest at pH 5.0 in the given pH values, and they were readily handled by precipitation and filtration. Especially E2 was able to be covalently incorporated into humic constituents to generate new humified co-polymers, thereby accelerating E2 humification and detoxification. These findings demonstrate that pH exhibits a far-reaching influence on the conversion kinetics, humification degrees, and products distribution of E2 and HAs in Tvlac-reinforced polyreaction. Thus, there is need to reappraise the fate and transport of estrogens with HAs present in natural water at varying pH levels.

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Molecular Properties and Reaction Mechanism of Multicopper Oxidases Related to Their Use in Biofuel Cells

Cited by 5 publications

References 109 publications

Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism

Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism

Stepwise Protonation and Electron-Transfer Reduction of a Primary Copper–Dioxygen Adduct

Effect of Two Humic Acids on Laccase-Driven 17β-Estradiol Conversion Kinetics and Polymerization Products at Varying pH Levels

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