Magnetic Resonance Studies of Manganese (II) Binding Sites of Pyruvate Kinase

Reuben, Jacques; Cohn, Mildred

doi:10.1016/s0021-9258(18)62567-0

Cited by 185 publications

(40 citation statements)

References 35 publications

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“…The temperature dependence for k act is steep (Figure C, black points), and yields a large activation enthalpy, 106 kJ/mol. This value is much higher than the 25–40 kJ/mol, typical for metal ion deprotonation in water, as estimated from the activation energies of water exchange processes for metal aqua complexes − or for enzyme-bound Mn(II), , and likely reflects a protein conformation change coupled to the Mn(II)–OH 2 deprotonation. An interesting precedent is offered by rhodopsin, which is activated by proton transfer from the retinal Schiff base to a protein acceptor, followed by conformation change of the protein.…”

Section: Resultsmentioning

confidence: 70%

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: 70%

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 value of tc was estimated to be about 1 X 10~s s in order to yield relative 13C metal ion distances of the substrate analogues. This tc value is based on t" which is calculated from the Bloembergen-Morgan equation (Bloembergen & Morgan, 1961) with a value for t" of 5 X 10"13 (Reuben & Cohn, 1970), and on values, which were estimated by comparison to comparable molecular weight complexes. In the case of O-phospho-D-serine and 3-nitropropionate, the analogues appear to be interacting with the metal ion through the C-l carboxyl end with no other group interacting directly.…”

Section: Discussionmentioning

confidence: 99%

L-Aspartase from Escherichia coli: substrate specificity and role of divalent metal ions

Falzone¹,

Karsten²,

Conley³

et al. 1988

Biochemistry

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The enzyme L-aspartase from Escherichia coli has an absolute specificity for its amino acid substrate. An examination of a wide range of structural analogues of L-aspartic acid did not uncover any alternate substrates for this enzyme. A large number of competitive inhibitors of the enzyme have been characterized, with inhibition constants ranging over 2 orders of magnitude. A divalent metal ion is required for enzyme activity above pH 7, and this requirement is met by many transition and alkali earth metals. The binding stoichiometry has been established to be one metal ion bound per subunit. Paramagnetic relaxation studies have shown that the divalent metal ion binds at the recently discovered activator site on L-aspartase and not at the enzyme active site. Enzyme activators are bound within 5 A of the enzyme-bound divalent metal ion. The activator site is remote from the active site of the enzyme, since the relaxation of inhibitors that bind at the active site is not affected by paramagnetic metal ions bound at the activator site.

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“…was obtained for £v in a study of the Mn2+-pyruvate kinase complex. 48 In the present study £v can hardly be smaller than 3 kcal/mol since this corresponds to values for and tv which are rather unlikely. Thus, for £v = 2.7 kcal/mol the values of and (298 K) obtained by the fit are 740 G and 1.8 X 10~n sec, respectively, both of which are incompatible with the above-mentioned EPR results.43•44 It is therefore reasonable to assume, that the correct value of £v for the complex studied here is in the range of 3.0-4.5 kcal/ mol.…”

Section: Resultsmentioning

confidence: 49%

Carbon-13 relaxation in paramagnetic complexes of amino acids. Structural and dynamical information on a manganese(II) complex of histidine

Led¹,

Grant²

1975

J. Am. Chem. Soc.

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The carbon-13 relaxation (Ti and Tf) and the carbon-13 isotropic contact shift of histidine in aqueous solution at pH 10.5, caused by the presence of Mn2+ ions in low concentrations, have been measured. For all six histidine carbons the T\ relaxation times were measured at least at two temperatures (310 and 343 K) while the temperature variation of the T2 relaxation times of the same atoms, as well as the isotropic contact shift for five of the histidine carbons and the water protons, were measured over a temperature range of 70-80°C. From these results the number of histidine molecules in the coordination sphere of the metal ions and the coupling constants for the hyperfine interaction between the unpaired electrons and the individual carbon-13 nuclei in these molecules have been evaluated, as well as the kinetic parameters for the exchange of the histidine ligands between the coordination sphere and the bulk histidine solution. Furthermore, it is found that the experimental results can be interpreted in terms of the model of Bloembergen and Morgan, according to which the electronic relaxation is caused by collision modulation of a transient zero field splitting (ZFS) interaction. Thus, the experimental results have yielded information about the ZFS interaction and the electronic relaxation and its temperature dependence. Likewise, estimated values of the correlation time for the molecular diffusional rotation and its activation energy have been obtained. Based on these results it has been concluded, that while the spin-lattice relaxation of the carbon-13 nuclei caused by the unpaired electrons is due to the dipolar interaction only, the paramagnetic contribution to the carbon-13 spin-spin relaxation is primarily controlled by scalar interaction. Finally, it is found that the distances between the Mn2+ ion and the individual carbon atoms in the ligand evaluated from the dipolar relaxation terms are in agreement with an octahedrally coordinated Mn2+ complex and correspond, with a single exception, closely to the distances expected from the crystal structure of the bis(histidino)-nickel(II) complex. The experimental accuracy of the structural parameters obtained by this method for a metal complex in solution is found to be comparable to the accuracy of X-ray structures of similar compounds in the crystal phase.

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Magnetic Resonance Studies of Manganese (II) Binding Sites of Pyruvate Kinase

Cited by 185 publications

References 35 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

L-Aspartase from Escherichia coli: substrate specificity and role of divalent metal ions

Carbon-13 relaxation in paramagnetic complexes of amino acids. Structural and dynamical information on a manganese(II) complex of histidine

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