Showing papers on "Purple acid phosphatases published in 1989"

Mössbauer analysis of the binuclear iron site in purple acid phosphatase from pig allantoic fluid

Abstract: We present a quantitative analysis of the Mossbauer spectra of the spin-coupled two-iron center in porcine purple acid phosphatase. The active enzyme contains a high-spin Fe(III)-Fe(II) pair with a ground state of effective spin S = /and g tensor g = (1.56, 1.72, 1.93), while the oxidized, inactive enzyme contains a high-spin Fe(III)-Fe(III) pair with a diamagnetic ground state. The Mossbauer spectra of reduced enzyme recorded at 4.2 K show complex magnetic hyperfine splittings, which have been parametrized in terms of the spin Hamiltonian H =βsgb + ∑SAI + ∑IPI-∑iiβNgniibis = /, where i = A and B labels the ferric and ferrous site, respectively. The fitting parameters g and Acan, in turn, be related to the intrinsic tensors gand aof the ferric and ferrous ions, respectively, assuming the coupling H =-2JSS + ∑SDS between the intrinsic spins S = /and S = 2. With the estimate-2J = 20 cm (Lauffer et al. J. Biol. Chem. 1983, 258, 14212–14218) and reasonable zero-field splittings Dthe model explains the low g values and the unusual anisotropy of the ferric hyperfine tensor aain the coupled representation. Explicit expressions for the tensors g and A are given to first order in D/J. this intermediate coupling model, |D/ J ≲ 1, is likely to apply to semimethemerythrins, methane monooxygenase, and other high-spin Fe(III)-Fe(II) couples with g values differing widely from g = 2 and to hold the key to a quantitative interpretation of susceptibility, ENDOR, and other magnetic properties. Preliminary data for metal-substituted and differentially enriched phosphatase are also presented. The parameters of the iron in the Fe-Zn enzyme are found to be close to the intrinsic parameters deduced from the analysis of the native Fe(III)-Fe(II) enzyme, a result that not only corroborates our model but also indicates little change in the iron environment on substitution of zinc. This result further suggests that in mixed-metal clusters the intrinsic properties of each iron site can be studied without the complexities arising from the exchange coupling.

Characteristics Of Bridging Oxo And Sulfido Groups In Multinuclear Iron Proteins

Abstract: The presence of oxo-bridged dinuclear iron clusters has been established in the respiratory protein, hemerythrin (Hr), and in the DNA-biosynthesis regulatory enzyme, ribonucleotide reductase (Rr). For the iron proteins uteroferrin and purple acid phosphatase (PAP) evidence for μ-oxo-bridged centers is less clear. Resonance Raman (RR) spectra obtained by excitation into an 0(2-) → Fe(III) CT band may show strong symmetric and weak antisymmetric Fe-0-Fe vibrational modes. We have investigated the spectra of a variety of μ-oxo-bridged Fe(III) complexes to establish the dependence of Raman scattering intensities upon structural parameters. Intensities were found to relate to the nature of the ligand trans to the oxo group: nitrogen ligands with unsaturation (e.g., pyrazole and imidazole) lead to strong scattering, whereas saturated ligands provide only poor scattering. The Fe-0 bonds in Hr and Rr are strong scatterers; the former is known from x-ray crystallography to have a histidyl ligand trans to the μ-oxo group. On this basis, a similar ligand structure is likely in the reductase. In contrast, PAP shows no oxo-bridge with UV and near-UV excitation. We propose that a different structural framework is necessary to account for this result. Hydrogen bonding of protein side chains to oxo and sulfido ligands is proposed to explain changes in frequencies for samples dissolved in water vs. D20. Differences in hydrogen-bond strengths between 0...(D) and S...(D) systems are transferred to the observed Fe-0 and Fe-S bond vibrations.