Filtyp
The sayings of the Desert Fathers had an important role in the monastic education and were very widespread. Originally written down in Greek, they were soon translated into all the main languages in the medieval Europe, and underwent transformations as they were copied. The sayings were organized in different ways, mainly alphabetically or according to themes, and as they were copied the repertoir
In his history of Swedish poets who wrote in (Humanist) Greek (1785–9), Matthias Floderus claimed that before his time such a mania for versification raged in the Swedish universities in Uppsala, Turku, Tartu, and Lund that hardly one academic specimen appeared without it being embellished with Greek verses by students – also prose texts occur. That claim is only slightly exaggerated. This paper p
Enzymes of the xanthine oxidase family are among the best characterized mononuclear molybdenum enzymes. Open questions about their mechanism of transfer of an oxygen atom to the substrate remain. The enzymes share a molybdenum cofactor (Moco) with the metal ion binding a molybdopterin (MPT) molecule via its dithiolene function and terminal sulfur and oxygen groups. For xanthine dehydrogenase (XDH)
The xanthine oxidase (XO) family comprises molybdenum-dependent enzymes that usually form homodimers (or dimers of heterodimers/trimers) organized in three domains that harbor two [2Fe-2S] clusters, one FAD, and a Mo cofactor. In this work, we crystallized an unusual member of the family, the periplasmic aldehyde oxidoreductase PaoABC from Escherichia coli. This is the first example of an E. coli
The class of [NiFe]-hydrogenases comprises oxygen-sensitive periplasmic (PH) and oxygen-tolerant membrane-bound (MBH) enzymes. For three PHs and four MBHs from six bacterial species, structural features of the nickel-iron active site of hydrogen turnover and of the iron-sulfur clusters functioning in electron transfer were determined using X-ray absorption spectroscopy (XAS). Fe-XAS indicated surp
[FeFe]-hydrogenase from green algae (HydA1) is the most efficient hydrogen (H2) producing enzyme in nature and of prime interest for (bio)technology. Its active site is a unique six-iron center (H-cluster) composed of a cubane cluster, [4Fe4S]H, cysteine-linked to a diiron unit, [2Fe]H, which carries unusual carbon monoxide (CO) and cyanide ligands and a bridging azadithiolate group. We have probe
The [FeFe]-hydrogenase (HydA1) from green algae is the minimal enzyme for efficient biological hydrogen (H2) production. Its active-site six-iron center (H-cluster) consists of a cubane, [4Fe4S]H, cysteine-linked to a diiron site, [2Fe]H. We utilized the spin-polarization of the iron Kβ X-ray fluorescence emission to perform site-selective X-ray absorption experiments for spectral discrimination o
Sulfite oxidase (SO) is an essential molybdoenzyme for humans, catalyzing the final step in the degradation of sulfur-containing amino acids and lipids, which is the oxidation of sulfite to sulfate. The catalytic site of SO consists of a molybdenum ion bound to the dithiolene sulfurs of one molybdopterin (MPT) molecule, carrying two oxygen ligands, and is further coordinated by the thiol sulfur of
The molybdenum cofactor is an important cofactor, and its biosynthesis is essential for many organisms, including humans. Its basic form comprises a single molybdopterin (MPT) unit, which binds a molybdenum ion bearing three oxygen ligands via a dithiolene function, thus forming Mo-MPT. In bacteria, this form is modified to form the bis-MPT guanine dinucleotide cofactor with two MPT units coordina
Two crystallized [FeFe] hydrogenase model complexes, 1 = (μ-pdt)[Fe(CO)2(PMe3)]2 (pdt = SC1H 2C2H2C3H2S), and their bridging-hydride (Hy) derivative, [1Hy]+ = [(μ-H)(μ-pdt)[Fe(CO)2 (PMe 3)]2]+ (BF4-), were studied by Fe K-edge X-ray absorption and emission spectroscopy, supported by density functional theory. Structural changes in [1Hy]+ compared to 1 involved small bond elongations (<0.03 Å) and
High-resolution X-ray absorption spectroscopy with narrow-band X-ray emission detection, supported by density functional theory calculations (XAES-DFT), was used to study a model complex, ([Fe2(μ-adt)(CO) 4(PMe3)2] (1, adt = S-CH2-(NCH 2Ph)-CH2-S), of the [FeFe] hydrogenase active site. For 1 in powder material (1powder), in MeCN solution (1′), and in its three protonated states (1H, 1Hy, 1HHy; H
The active site for hydrogen production in [FeFe] hydrogenase comprises a diiron unit. Bioinorganic chemistry has modeled important features of this center, aiming at mechanistic understanding and the development of novel catalysts. However, new assays are required for analyzing the effects of ligand variations at the metal ions. By high-resolution X-ray absorption spectroscopy with narrow-band X-
Cryogenic illumination of Photosystem II (PSII) can lead to the trapping of the metastable radical Y Z •, the radical form of the redox-active tyrosine residue D1-Tyr161 (known as Y Z). Magnetic interaction between this radical and the CaMn 4 cluster of PSII gives rise to so-called split electron paramagnetic resonance (EPR) signals with characteristics that are dependent on the S state. We report
Ribonucleotide reductases (RNRs) are essential for DNA synthesis in most organisms. In class-Ic RNR from Chlamydia trachomatis (Ct), a MnFe cofactor in subunit R2 forms the site required for enzyme activity, instead of an FeFe cofactor plus a redox-active tyrosine in class-Ia RNRs, for example in mouse (Mus musculus, Mm). For R2 proteins from Ct and Mm, either grown in the presence of, or reconsti
Irreversible inhibition by molecular oxygen (O 2) complicates the use of [FeFe]-hydrogenases (HydA) for biotechnological hydrogen (H 2) production. Modification by O 2 of the active site six-iron complex denoted as the H-cluster ([4Fe4S]-2Fe H) of HydA1 from the green alga Chlamydomonas reinhardtii was characterized by x-ray absorption spectroscopy at the iron K-edge. In a time-resolved approach,
Ten square-based pyramidal molybdenum complexes with different sulfur donor ligands, that is, a variety of dithiolenes and sulfides, were prepared, which mimic coordination motifs of the molybdenum cofactors of molybdenum-dependent oxidoreductases. The model compounds were investigated by Mo K-edge X-ray absorption spectroscopy (XAS) and (with one exception) their molecular structures were analyze
YedY from Escherichia coli is a new member of the sulfite oxidase family of molybdenum cofactor (Moco)-containing oxidoreductases. We investigated the atomic structure of the molybdenum site in YedY by X-ray absorption spectroscopy, in comparison to human sulfite oxidase (hSO) and to a MoIV model complex. The K-edge energy was indicative of MoV in YedY, in agreement with X-and Q-band electron para
