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排序方式: 共有86条查询结果,搜索用时 145 毫秒
81.
Jung C Schünemann V Lendzian F 《Biochemical and biophysical research communications》2005,338(1):355-364
Since the discovery of cytochromes P450 and their assignment to heme proteins a reactive iron-oxo intermediate as the hydroxylating species has been discussed. It is believed that the electronic structure of this intermediate corresponds to an iron(IV)-porphyrin-pi-cation radical system (Compound I). To trap this intermediate the reaction of P450 with oxidants (shunt pathway) has been used. The common approaches are stopped-flow experiments with UV-visible spectroscopic detection or rapid-mixing/freeze-quench studies with EPR and M?ssbauer spectroscopic characterization of the trapped intermediate. Surprisingly, the two approaches seem to give conflicting results. While the stopped-flow data indicate the formation of a porphyrin-pi-cation radical, no such species is seen by EPR spectroscopy, although the M?ssbauer data indicate iron(IV) for P450cam (CYP101) and P450BMP (CYP102). Instead, radicals on tyrosine and tryptophan residues are observed. These findings are reviewed and discussed with respect to intramolecular electron transfer from aromatic amino acids to a presumably transiently formed porphyrin-pi-cation radical. 相似文献
82.
Schünemann V Lendzian F Jung C Contzen J Barra AL Sligar SG Trautwein AX 《The Journal of biological chemistry》2004,279(12):10919-10930
We report a multifrequency (9.6-, 94-, 190-, and 285-GHz) EPR study of a freeze-quenched intermediate obtained from reaction of substrate-free cytochrome P450cam (CYP101) and its Y96F and Y96F/Y75F mutants with peroxy acids. It is generally assumed that in such a shunt reaction an intermediate [Fe(IV)=O, porphyrin-pi-cation radical] is formed, which should be identical to the species in the natural reaction cycle. However, for the wild type as well as for the mutant proteins, a porphyrin-pi-cation radical is not detectable within 8 ms. Instead, EPR signals corresponding to tyrosine radicals are obtained for the wild type and the Y96F mutant. Replacement of both Tyr-96 and Tyr-75 by phenylalanine leads to the disappearance of the tyrosine EPR signals. EPR studies at 285 GHz on freeze-quenched wild type and Y96F samples reveal g tensor components for the radical (stretched g(x) values from 2.0078 to 2.0064, g(y) = 2.0043, and g(z) = 2.0022), which are fingerprints for tyrosine radicals in a heterogeneous polar environment. The measurements at 94 GHz using a fundamental mode microwave resonator setup confirm the 285-GHz study. From the simulation of the hyperfine structure in the 94-GHz EPR spectra the signals have been assigned to Tyr-96 in the wild type and to Tyr-75 in the Y96F mutant. We suggest that a transiently formed Fe(IV)=O porphyrin-pi-cation radical intermediate in P450cam is reduced by intramolecular electron transfer from these tyrosines within 8 ms. 相似文献
83.
84.
Johannes Fritsch Elisabeth Siebert Jacqueline Priebe Ingo Zebger Friedhelm Lendzian Christian Teutloff B?rbel Friedrich Oliver Lenz 《The Journal of biological chemistry》2014,289(11):7982-7993
The membrane-bound [NiFe] hydrogenase (MBH) supports growth of Ralstonia eutropha H16 with H2 as the sole energy source. The enzyme undergoes a complex biosynthesis process that proceeds during cell growth even at ambient O2 levels and involves 14 specific maturation proteins. One of these is a rubredoxin-like protein, which is essential for biosynthesis of active MBH at high oxygen concentrations but dispensable under microaerobic growth conditions. To obtain insights into the function of HoxR, we investigated the MBH protein purified from the cytoplasmic membrane of hoxR mutant cells. Compared with wild-type MBH, the mutant enzyme displayed severely decreased hydrogenase activity. Electron paramagnetic resonance and infrared spectroscopic analyses revealed features resembling those of O2-sensitive [NiFe] hydrogenases and/or oxidatively damaged protein. The catalytic center resided partially in an inactive Niu-A-like state, and the electron transfer chain consisting of three different Fe-S clusters showed marked alterations compared with wild-type enzyme. Purification of HoxR protein from its original host, R. eutropha, revealed only low protein amounts. Therefore, recombinant HoxR protein was isolated from Escherichia coli. Unlike common rubredoxins, the HoxR protein was colorless, rather unstable, and essentially metal-free. Conversion of the atypical iron-binding motif into a canonical one through genetic engineering led to a stable reddish rubredoxin. Remarkably, the modified HoxR protein did not support MBH-dependent growth at high O2. Analysis of MBH-associated protein complexes points toward a specific interaction of HoxR with the Fe-S cluster-bearing small subunit. This supports the previously made notion that HoxR avoids oxidative damage of the metal centers of the MBH, in particular the unprecedented Cys6[4Fe-3S] cluster. 相似文献
85.
O. Trofanchuk M. Stein Ch. Geßner F. Lendzian Y. Higuchi W. Lubitz 《Journal of biological inorganic chemistry》2000,5(1):36-44
The Ni-A and the Ni-B forms of the [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F have been studied in single crystals by continuous wave and pulsed EPR spectroscopy at different temperatures (280?K, 80?K, and 10?K). For the first time, the orientation of the g-tensor axes with respect to the recently published atomic structure of the active site at 1.8?Å resolution was elucidated for Ni-A and Ni-B. The determined g-tensors have a similar orientation. The configuration of the electronic ground state is proposed to be Ni(III) 3d 1 z2 for Ni-A and Ni-B. The g z principal axis is close to the Ni-S(Cys549) direction; the g x and the g y axes are approximately along the Ni-S(Cys546) and Ni-S(Cys81) bonds, respectively. It is proposed that the difference between the Ni-A and Ni-B states lies in a protonation of the bridging ligand between the Ni and the Fe. 相似文献
86.