Proton NMR investigation into the basis for the relatively high redox potential of lignin peroxidase

A two-dimensional NMR study of Co(II)7 rabbit liver metallothionein

The 600-MHz 1H-NMR NOESY spectra on Co(II)7-reconstituted metallothionein (Co7MT), exhibiting hyperfine signals in the range 350 ppm to -50 ppm, with nuclear relaxation times of the order of a few milliseconds, have been measured and several interproton connectivities have been detected. To our knowledge, this is the largest spectral window ever reported for a two-dimensional 1H-NMR spectrum in the case of a paramagnetic metalloprotein. No scalar connectivities could be detected. The hyperfine-shifted signals belong to the cysteine-ligand protons of the Co4S11 cluster of Co7MT. Together with results from one-dimensional NOE experiments, the two-dimensional experiments allowed us to proceed with the pairwise assignment of the isotropically shifted signals of the C beta H2 groups of the metal-coordinated cysteines. With the aid of computer-graphics inspection of the four-metal-cluster domain, based on the NMR solution structure of Cd7MT, it is possible to purpose sequence-specific assignments of a few hyperfine-shifted 1H-NMR signals. In particular, a tentative assignment is given for the six signals whose shifts exhibit an antiCurie temperature dependence. The assignment relies on the theoretical model that qualitatively rationalizes the isotropic-shift pattern and its temperature dependence. Inferences on the solution structure of the Co4S11 cluster are drawn.

Haloperoxidase activity of Phanerochaete chrysosporium lignin peroxidases H2 and H8

Monochlorodimedone (MCD), commonly used as a halogen acceptor for haloperoxidase assays, was oxidized by hydrogen peroxide in the presence of lignin peroxidase isoenzymes H2 and H8. When oxidized, it produced a weak absorption band with an intensity that varied with pH. This absorbance was used as a simple method for the product analysis because it disappeared when MCD was brominated or chlorinated. We assessed the activity of the lignin peroxidases for oxidation of bromide by measuring the bromination of MCD, the formation of tribromide, the bromide-mediated oxidation of glutathione, and the bromide-mediated catalase-like activity. We analyzed the reaction products of MCD and the halide-mediated oxidation of glutathione when bromide was replaced by chloride. These enzymes demonstrated no significant activity for oxidation of chloride. Unlike other peroxidases, the lignin peroxidases exhibited similar pH-activity curves for the iodide and bromide oxidations. The optimum pH for activity was about 2.5. Surprisingly, this pH dependence of lignin peroxidase activity for the halides was nearly the same in the reactions with hydrogen donors, such as hydroquinone and guaiacol. The results suggested that protonation of the enzymes with pKa approximately 3.2 is necessary for the catalytic function of lignin peroxidases, irrespective of whether the substrates are electron or hydrogen donors. These unique reaction profiles of lignin peroxidases are compared to those of other peroxidases, such as lactoperoxidase, bromoperoxidase, chloroperoxidase, and horseradish peroxidase. Isozyme H2 was more active than isozyme H8, but isozyme H8 was more stable at very acidic pH.

Non-equivalent natures of the coordinated imidazole rings of cytochrome c3 from D. vulgaris Miyazaki F as studied by 1H NMR

All of the C2 proton signals of the coordinated histidine residues in the 1H NMR spectrum of cytochrome c3 from D. vulgaris Miyazaki F were assigned by specific deuteration. They appeared at extremely high fields and scattered in a wide range from -4 to -22 ppm. This clearly shows that the chemical properties of the imidazole groups are quite different from one another. The extremely high-field shift of the C2 signal indicates that some of them must carry the imidazolate-like nature to some extent. This might be responsible for the extremely low redox potentials of the four hemes. On changing temperature, most of them showed Curie-type change. All of the C2 signals showed a small p2H dependence in the range of p2H 4.8-10.0.

NOE and two-dimensional correlated 1H-NMR spectroscopy of cytochrome c' from Chromatium vinosum

1H two-dimensional (nuclear Overhauser effect spectroscopy (NOESY) and two-dimensional correlated spectroscopy (COSY) spectra of cytochrome c' from Chromatium vinosum have been obtained. The protein is of medium size (Mr 28,000), essentially high spin (S = 5/2) although some quantum mechanical spin admixing with S = 3 2 may be present. Under these circumstances NOESY cross peaks have been revealed between geminal protons (alpha-CH2 propionate and beta-CH2 protons of the bound histidine) and between alpha-CH2 propionate protons and the heme methyl groups. COSY maps have confirmed the geminal nature of the proton pairs, even with a linewidth as large as 900 Hz; the J value is about 12 Hz. This assignment has rationalized on a sound basis the biochemical behavior of this protein with pH and has showed the utility of this kind of spectroscopy for the other cytochromes c' structures and analogous systems.