The novel “g' = 1.74” EPR spectrum of pink and purple uteroferrin.

Antanaitis, B C; Aisen, Philip; Lilienthal, H. R.; Roberts, R. M.; Bazer, Fuller W.

doi:10.1016/s0021-9258(19)70276-2

Cited by 50 publications

(23 citation statements)

References 42 publications

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“…Aerobic purification results in isolation of mammalian purple acid phosphatase in the purple (λ max ≈ 550 nm) Fe 3+ -Fe 3+ state which is catalytically inactive (e5% activity, vide infra). Treatment of the purple form with mild reductants, e.g., BME or ascorbate, yields the pink form (λ max ≈ 510 nm) that is catalytically active and exhibits an EPR spectrum with g-values of 1.94, 1.76, and 1.56 from the dinuclear iron cluster in the mixed valence Fe 3+ -Fe 2+ oxidation state (Davis & Averill, 1982;Antanaitis et al, 1980Antanaitis et al, , 1983Averill et al, 1987). Interconversion between the Fe 3+ -Zn 2+ and Fe 3+ -Fe 2+ forms in the purple acid phosphatases is readily achieved (Antanaitis et al, 1983;Beck et al, 1988;David & Que, 1990), and this procedure has been used to replace Zn 2+ in bovine brain calcineurin with Fe 2+ to yield a dinuclear Fe 3+ -Fe 2+ center which also exhibits a mixed valence EPR signal with g av < 2.0 (Yu et al, 1995).…”

Section: Discussionmentioning

confidence: 99%

“…Various metal ions can apparently be accommodated by the β-R-β-R-β fold although there are a few systematic studies which have identified either the physiologic metal ions or the most catalytically efficient ones. In the purple acid phosphatases, the Fe 3+ -Fe 2+ and Fe 3+ -Zn 2+ forms have been characterized and appear to have nearly identical catalytic activities (Keough et al, 1980;Antanaitis et al, 1980). In these enzymes, the Fe 3+ ion is situated in the M1 site as evidenced by the presence of a tyrosine-to-Fe 3+ charge transfer band in the 500-550 nm region of the visible spectrum (Kurtz,2 The motif in the plant and mammalian purple acid phosphatases, D(X)nGDXXY(X)mGNHD/E, represents a variation of the phosphoesterase motif.…”

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confidence: 99%

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Spectroscopic and Enzymatic Characterization of the Active Site Dinuclear Metal Center of Calcineurin: Implications for a Mechanistic Role

Golbeck

Yao

et al. 1997

Biochemistry

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The active site of bovine brain calcineurin contains an Fe3+-Zn2+ dinuclear metal center. Replacement of Zn2+ with Fe2+ yields a mixed valence Fe3+-Fe2+ center that exhibits a characteristic EPR signal that can be used as a convenient spectroscopic probe of the active site. Addition of product phosphate to both the Fe3+-Fe2+ and Fe3+-Zn2+ forms of calcineurin led to perturbations of the respective EPR signals, indicating that phosphate affects the environment of the paramagnetic centers. Anaerobic titrations of the iron-substituted Fe3+-Fe2+ enzyme with dithionite resulted in a gradual loss of activity toward pNPP that paralleled the loss of intensity of the EPR signal of the mixed valence diiron center. During dithionite reduction, an EPR resonance with g approximately 12 appeared. The intensity of this resonance increased when the spectrum was recorded in a parallel mode cavity and was therefore attributed to a paramagnetic center with integer spin. Oxidation of the Fe3+-Fe2+ cluster to the diferric state by hydrogen peroxide also led to a loss of activity. These results indicate that the mixed valence oxidation state represents the catalytically competent form of the cluster. The dependence of the enzyme activity on the redox state of the cluster has implications for a mechanistic role.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Spectroscopic and Enzymatic Characterization of the Active Site Dinuclear Metal Center of Calcineurin: Implications for a Mechanistic Role

Golbeck

Yao

et al. 1997

Biochemistry

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“…This can be understood since expression 8 does not take into account the effects of the ZFS on the eigenstates of ℋ ex . The appreciable ZFS from Fe 2+ perturbs the weak exchange interaction and mixes its ground state with higher spin manifolds, giving rise to low g̃ eff values. ,, For example, EPR g̃ eff tensors with components lower than the spin-only value are characteristic of the spin ground states of some mixed-valence diiron−oxo proteins, , such as reduced uteroferrin , and semimet-hemerythrin …”

Section: Discussionmentioning

confidence: 99%

Mössbauer Spectroscopy of Spin-Coupled Iron−Chromium Complexes: μ-Hydroxo−Bis(μ-acetato)-Bridged Iron(2+)−Chromium(3+) and μ-Oxo−Bis(μ-acetato)-Bridged Iron(3+)−Chromium(3+)

1996

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We have analyzed Mössbauer spectra of a model complex of known structure with an Fe2+(S 1=2)−μOH−Cr3+(S 2=3/2) center (A) and of its Fe3+(S 1 = 5/2)−μO−Cr3+(S 2=3/2) analog (B). These μ-hydroxo and μ-oxo bridged binuclear metal centers display unusual magnetic properties as found in several diiron−oxo proteins. Our results confirm antiferromagnetic spin coupling between Fe and Cr ions which results in S eff = 1/2 and S eff = 1 ground states for A and B, respectively. The isotropic exchange ℋex = J S 1·S 2 is weaker for the μ-hydroxo (J ≈ 21 cm-1) than for the μ-oxo (J ≈ 275 cm-1) complex. Spectra recorded at 4.2 K, in fields of 0.22−4.7 T, have been analyzed with the effective spin Hamiltonian for the ground state ℋeff = βS eff·g̃ eff·H + + I 1·P̃ 1·I 1 − β ngn H·I 1. For complex B, the zero-field splitting S eff·D̃ eff·S eff is also included in ℋeff. In applied fields, the 4.2 K spectra of Fe2+ in A showed hyperfine splittings which allowed the determination of the following S eff = 1/2 Hamiltonian parameters: 1/3 Tr g̃ eff ≈ 2.00, = −(18.3,5.6,25.0) T, ΔEQ = +2.87 mm/s, η = 0.93, and δFe = 1.21 mm/s. The weak coupling of A allows the zero-field splitting to mix higher spin manifolds with the ground state doublet, and, to obtain intrinsic parameters, we also calculated the spectra of Fe2+ by diagonalizing the (2S 1 + 1 = 5) × (2S 2 + 1 = 4) matrix of the Hamiltonian ℋ = J S 1·S 2 + + βS i ·g̃i ·H} + S 1·ã 1·I 1 + I 1·P̃ 1·I 1 − β ngn H·I 1. We determined the following parameters for Fe2+: D 1 = +4.0 cm-1, E 1 = +0.4 cm-1, 1/3 Tr g̃ 1 ≳ 2.07, ã 1/gn β n = −(10.2,3.5,15.6) T. For complex B, we found that Fe3+ has a large quadrupole splitting (ΔEQ = −2.00 mm/s, η = 0.22) presumably as a result of anisotropic covalency due to the close proximity of the bridging O2-. This large ΔE Q is comparable to values found in diiron−oxo proteins. Spectra of B in applied fields also displayed hyperfine splittings, and the following S eff = 1 Hamiltonian parameters could be deduced: D eff = +3.9 cm-1, E eff = +1.7 cm-1, 1/3 Tr g̃ eff = 2.01, = −(33.8,30.9,35.8) T, δFe = 0.52 mm/s.

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“…EPR spectra taken between 1.4 and 4.2 K were recorded with a Varían E-9 spectrometer equipped with a Varían E-245 double Dewar apparatus. The temperature was varied as previously described (Antanaitis et al, 1980). Saturation of the EPR resonances was avoided by studying samples in a range where the EPR signal intensity was proportional to the square root of the microwave power.…”

Section: Methodsmentioning

confidence: 99%

Electron paramagnetic resonance and magnetic susceptibility studies of dimanganese concanavalin A. Evidence for antiferromagnetic exchange coupling

Antanaitis

Brown²,

Chasteen

et al. 1987

Biochemistry

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The double Mn2+ complex of concanavalin A with bound saccharide (SMMPL) was examined by electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements. A room temperature X-band (9 GHz) EPR spectrum of SMMPL revealed a relatively weak, broad resonance in contrast to the spectrum with a six-line hyperfine-split pattern observed for the mononuclear, high-spin Mn2+ complex found in Ca2+-Mn2+-concanavalin A with saccharide present (SCMPL). The EPR spectrum of SMMPL at 77 K, however, consisted of a series of overlapping patterns of 11 hyperfine-split lines near g = 2.0 with members of each pattern separated by 47 G, half the value of the hyperfine splitting of SCMPL. These 11-line patterns are preserved at Q-band (35 GHz), indicating that the manganese ions in SMMPL form a spin-coupled, binuclear center. As expected for an exchange-coupled system, the EPR signal of SMMPL at 77 K saturates at a higher microwave power than those for SCMPL or Mn2+ aquoion. There is also a marked loss of EPR signal intensity for SMMPL between 4.2 and 1.4 K, which supports the view that the pair of manganese ions is exchanged-coupled. The temperature dependence of both the magnetic susceptibility and the low-temperature EPR spectral intensity can be explained by a model in which the two high-spin Mn2+ ions of SMMPL are antierromagnetically exchanged-coupled with an isotropic coupling constant J = 1.8 cm-1 (for the spin Hamiltonian Hex = JS1.S2). Zero-field splitting D' was estimated to be 375 G from the EPR spectrum.(ABSTRACT TRUNCATED AT 250 WORDS)

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The novel “g' = 1.74” EPR spectrum of pink and purple uteroferrin.

Cited by 50 publications

References 42 publications

Spectroscopic and Enzymatic Characterization of the Active Site Dinuclear Metal Center of Calcineurin: Implications for a Mechanistic Role

Spectroscopic and Enzymatic Characterization of the Active Site Dinuclear Metal Center of Calcineurin: Implications for a Mechanistic Role

Mössbauer Spectroscopy of Spin-Coupled Iron−Chromium Complexes: μ-Hydroxo−Bis(μ-acetato)-Bridged Iron(2+)−Chromium(3+) and μ-Oxo−Bis(μ-acetato)-Bridged Iron(3+)−Chromium(3+)

Electron paramagnetic resonance and magnetic susceptibility studies of dimanganese concanavalin A. Evidence for antiferromagnetic exchange coupling

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