Pinpointing a Mechanistic Switch Between Ketoreduction and “Ene” Reduction in Short‐Chain Dehydrogenases/Reductases

Three enzymes of the Mentha essential oil biosynthetic pathway are highly homologous, namely the ketoreductases (?)‐menthone:(?)‐menthol reductase and (?)‐menthone:(+)‐neomenthol reductase, and the “ene” reductase isopiperitenone reductase. We identified a rare catalytic residue substitution in the last two, and performed comparative crystal structure analyses and residue‐swapping mutagenesis to investigate whether this determines the reaction outcome. The result was a complete loss of native activity and a switch between ene reduction and ketoreduction. This suggests the importance of a catalytic glutamate vs. tyrosine residue in determining the outcome of the reduction of α,β‐unsaturated alkenes, due to the substrate occupying different binding conformations, and possibly also to the relative acidities of the two residues. This simple switch in mechanism by a single amino acid substitution could potentially generate a large number of de novo ene reductases.     

Synthesis and characterization of new Co(III) mixed-ligand complexes,containing 2-hydroxy-aryloximes and α-diimines. Crystal and molecular structure of [Co(saox)(bipy)2]Br

A series of 12 cobalt (III) complexes of 2-hydroxy-aryloximes (H₂oxime) with an α-diimine (enR), under the general formula [Co(oxime)(enR)₂]Br · 2H₂O were synthesized and characterized. The IR and H NMR spectra indicate the bidentate coordination mode of the ligands and the dianionic character of the oxime ligand in the complexes, while the electronic excitation spectra are indicative of an octahedral geometry around cobalt(III). The octahedral environment with CoN₅O chromophore was confirmed by X-ray structure analysis of the solvated [bis(2,2′-bipyridine)-(2-hydroxy-benzaldoximato)cobalt(III)]bromide, [Co(saox)(bipy)₂]Br · 0.166bipy · 0.15CH₃OH · 1.75H₂O. The phenolic oxygen as well as the oximic nitrogen plus two nitrogen atoms, each one from a different bipy molecule, build the equatorial plane. The oximic chelate ring can be described as an extentend delocalized π system. The crystal structure of one of the investigated oxime ligands, the 2-hydroxy-benzophenonoxime (H₂bpox) was also determined by X-ray analysis, verifying the strong intra-and intermolecular hydrogen bonds.     

Free electron transfer from xanthenyl- and fluorenylsilanes (Me3 or Ph3) to parent solvent radical cations: effects of molecule dynamics

Parent radical cations of nonpolar solvents (alkanes and alkyl chlorides) ionize 9-(trimethylsilyl)xanthenes and 9-(trimethylsilyl)fluorenes in a diffusion-controlled electron transfer. The actual electron jump as the deciding part of the process does not require a defined encounter complex, and therefore the reactants are not subjected to any geometry optimization. Considering the molecule dynamics of the donors, bending motions of the silyl group are concerted with fluctuations of the highest occupied molecular orbital electrons. Ionizing such a standing conformer mixture creates metastable (microsecond) as well as dissociative donor radical cations. A mobility restriction of the benzylic silane group in positions vertical to the phenyl plane stabilizes the radical cations and accounts for a declining amount of dissociative radical cations, which undergo C-Si bond fragmentation in the order benzylsilane > xanthenylsilane > fluorenylsilane.     

Studies on pyrrolidinones. On the carbamoylation of some pyroglutamic derivatives

The carbamoylation of some lactams derivatived from pyroglutamic acid as been studied; better yields were obtained starting from the unsubstitued lactam (toluene, 80°) rather than starting with the N-silyllactam (room temperature), although these latter reaction conditions could be interesting for heat sensitive compounds. Methyl and phenyl isothiocyanate react only with the sodium salt of methyl pyroglutamate, giving 1,5-diaddition products.     

Studies on pyrrolidinones. Synthesis of some N-fatty acylpyroglutamic acids

Starting from readily available pyroglutamic acid 1 , some N-fatty acylpyroglutamic acids were synthesized and characterized by their spectral data. A preliminary pharmacological study showed that N-stearoylpyroglutamic acid 4c displays a CNS stimulating effect on mice.     

Recent research efforts in the area of biotechnology for fuels and chemicals

Applied Biochemistry and Biotechnology -     

TiO2 nanoparticles as a soft X-ray molecular probe

This communication reports the development of a TiO2-streptavidin nanoconjugate as a new biological label for X-ray bio-imaging applications; this new probe, used in conjunction with the nanogold probe, will make it possible to obtain quantitative, high-resolution information about the location of proteins using X-ray microscopy.     

J-Class Weighted Shifts on the Space of Bounded Sequences of Complex Numbers

We provide a characterization of J-class and J ^mix-class unilateral weighted shifts on in terms of their weight sequences. In contrast to the previously mentioned result we show that a bilateral weighted shift on cannot be a J-class operator. During this research the second author was fully supported by SFB 701 “Spektrale Strukturen und Topologische Methoden in der Mathematik" at the University of Bielefeld, Germany. He would also like to express his gratitude to Professor H. Abels for his support.     

Alteration of biological samples in speciation analysis of metalloproteins

For investigations of metalloproteins by speciation analysis, the integrity of the protein–metal complexes before and during separation is crucial. Knowledge about potential alterations of the samples is thus essential to avoid misinterpretations of the analytical results. Chromatographic element profiles of different cytosolic samples from animal tissues were measured repeatedly to estimate the sample stability. The dependence of the signals on the dwell time of the sample in an autosampling device at 4 °C for a period of 10 h was observed. Alterations in the element content of different metal-containing fractions were quantified by means of recovery values. Some metalloprotein fractions (e.g. ≈27-kDa arsenic, ≈27-kDa iron and different zinc fractions) were stable or only minor alterations were observed and for their investigation an autosampling device is therefore suitable. However, most of the other metalloprotein fractions, especially nickel-containing proteins, showed major alterations: these samples should therefore be analysed immediately after preparation or directly after thawing. Figure Chromatographic manganese-profiles of 11 repeated SEC-ICP-MS-separations of rat brain cytosol. The first sample at time 0 h was the run immediately started after thawing of the prepared cytosol; the other samples were measured hourly, taken from the same sample vial. In addition to the time axis the estimated molecular mass axis is plotted Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.