Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae

The binding affinity of the two substrate–water molecules to the water-oxidizing Mn₄CaO₅ catalyst in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae was studied in the S₂ and S₃ states by the exchange of bound ¹⁶O-substrate against ¹⁸O-labeled water. The rate of this exchange was detected via the membrane-inlet mass spectrometric analysis of flash-induced oxygen evolution. For both redox states a fast and slow phase of water-exchange was resolved at the mixed labeled m/z 34 mass peak: k_f = 52 ± 8 s^− 1 and k_s = 1.9 ± 0.3 s^− 1 in the S₂ state, and k_f = 42 ± 2 s^− 1 and k_slow = 1.2 ± 0.3 s^− 1 in S₃, respectively. Overall these exchange rates are similar to those observed previously with preparations of other organisms. The most remarkable finding is a significantly slower exchange at the fast substrate–water site in the S₂ state, which confirms beyond doubt that both substrate–water molecules are already bound in the S₂ state. This leads to a very small change of the affinity for both the fast and the slowly exchanging substrates during the S₂ → S₃ transition. Implications for recent models for water-oxidation are briefly discussed.     

Profiles of phenotype resistance to antibiotic other than β-lactams in Klebsiella pneumoniae ESBLs-producers, carrying blaSHV genes

Extended spectrum β-lactamases production is one of the most common mechanism of resistance to extended spectrum β-lactam antibiotics is increasing worldwide. Twenty five strains of Klebsiella pneumoniae isolated from clinical specimens were tested. Based on the phenotypic confirmatory test all these strains were defined as ESBL producers named ESBL(+). The plasmid DNA from each strains was used to investigate the presence of blaSHV genes responsible for extended spectrum β-lactamases production. Moreover, susceptibility of these strains to antibiotic other than β-lactams in was tested.     

Oxidative stress during aging of the yeast in a stationary culture and its attenuation by antioxidants

Oxidative stress during aging of Saccharomyces cerevisiae in stationary culture was documented by demonstration of progressive increase in the formation of superoxide, decrease in the content of acid‐soluble thiols and of acid‐soluble antioxidant capacity of cell extracts, and accumulation of aldehydes and protein carbonyl groups in two yeast strains and decreases in activities of antioxidant enzymes. Cells of a CuZn‐SOD (superoxide dismutase)‐1‐deficient strain showed a higher loss of viability than cells of an isogenic wild‐type strain. Cell survival was augmented, and changes in biochemical parameters were ameliorated, by addition of exogenous antioxidants (ascorbic acid, glutathione and melatonin) in both strains.     

Relationship between genotype and soil environment during colonization of poplar roots by mycorrhizal and endophytic fungi

Poplars are among the few tree genera that can develop both ectomycorrhizal (ECM) and arbuscular (AM) associations; however, variable ratios of ECM/AM in dual mycorrhizal colonizations were observed in the roots of a variety of poplar species and hybrids. The objective of our study was to analyze the effect of internal and external factors on growth and dual AM and ECM colonization of poplar roots in three 12–15-year-old common gardens in Poland. We also analyzed the abundance of nonmycorrhizal fungal endophytes in the poplar roots. The Populus clones comprised black poplars (Populus deltoides and P. deltoides × Populus nigra), balsam poplars (Populus maximowiczii × Populus trichocarpa), and a hybrid of black and balsam poplars (P. deltoides × P. trichocarpa). Of the three sites that we studied, one was located in the vicinity of a copper smelter, where soil was contaminated with copper and lead. Poplar root tip abundance, mycorrhizal colonization, and soil fungi biomass were lower at this heavily polluted site. The total mycorrhizal colonization and the ratio of ECM and AM colonization differed among the study sites and according to soil depth. The influence of Populus genotype was significantly pronounced only within the individual study sites. The contribution of nonmycorrhizal fungal endophytes differed among the poplar clones and was higher at the polluted site than at the sites free of pollution. Our results indicate that poplar fine root abundance and AM and ECM symbiosis are influenced by environmental conditions. Further studies of different site conditions are required to characterize the utility of poplars for purposes such as the phytoremediation of polluted sites.     

Chemoenzymatic resolution of racemic Wieland–Miescher and Hajos–Parrish ketones

Enantiospecific microbial reduction of bicyclic ketones was described. Racemic Wieland–Miescher (1) and Hajos–Parrish (2) ketones were used as substrates. In a 4-h biotransformation of Hajos–Parrish ketone (2) using the strain of Didymosphaeria igniaria an optically pure ketone (R)-2 was obtained, whereas the (S)-2 ketone underwent reduction to (4aS,5S)-4 alcohol with 100% of enantiomeric excess and with over 60% of diastereoisomeric excess. Jones oxidation of the alcohol obtained in the biotransformation gave an optically pure ketone (S)-2. Enzymatic system of Coryneum betulinum reduced the (R)-2 ketone to (4aR,5S)-4 alcohol with a high enantiomerical purity in a 6-day reaction. Wieland-Miescher (1) ketone was transformed by these microorganisms in an analogous way, but the reaction times were longer.     

Effects of different dietary fatty acids profiles on the growth performance and body composition of juvenile tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> (L.))

Juvenile tench (initial weight of about 57 g) were fed feed supplemented with fish oil (group FO), linseed oil (group LO), peanut oil (group PO), or rapeseed oil (group RO) containing 47% protein and 12% fat for 55 days. The inclusion of the tested oils was 50 g kg⁻¹ (42% total crude lipids in diets). No significant differences were noted in the fish growth performance. The proximate composition of the whole fish bodies and the viscera (water, protein, fat, ash) was similar in all the dietary treatments (P > 0.05). Differences were noted only with regard to the ash content of the fillets (P < 0.05). The analysis of the fatty acids profiles of tench (whole fish) indicated there were significant differences in the total content of monoenoic and polyenoic (PUFA) acids. Significant differences were also noted with regard to n-3 PUFA and n-6 PUFA. Consequently, the ratio of n-3/n-6 acids ranged from 1.6 (group PO) to 2.08 (group LO; P < 0.05). The feed applied was not confirmed to have had an impact on the fatty acids profile of the tench fillets. There was a statistically significant intergroup difference in the content of saturated fatty acids (SFA) in tench viscera. In the fish fed vegetable oils supplemented diets, the level of SFA was lower (P < 0.05).     

On the observation of a gem diol intermediate after O–O bond cleavage by extradiol dioxygenases. A hybrid DFT study

Catalytic cycle intermediates of a representative extradiol dioxygenase, homoprotocatechuate 2,3-dioxygenase (HPCD), have recently been characterized in crystallo by Kovaleva and Lipscomb. The structures of the identified species indicate that the process of inserting oxygen into the catechol ring occurs stepwise, and involves an Fe(II)-alkylperoxo intermediate and its O–O cleavage product: a gem diol species. In general, these findings corroborate the results of our previous computational studies; however, the fact that the gem diol species is stable enough to be observed in the crystal form seems to be at odds with the computational mechanistic data, which suggest that this intermediate should very readily and spontaneously convert to the epoxide species. The key question then becomes what is actually observed in the X-ray experiments. Here we report additional computational studies undertaken with the hope of clarifying this issue. The results obtained for active site models hosting both the native and the alternative (4-sulfonylcatechol) substrate indicate that the stability of the gem diol species is substantially increased if an electron and a proton are added. If this occurs somehow, the lifetime of the intermediate should be sufficient to observe it.     

Does molecular docking reveal alternative chemopreventive mechanism of activation of oxidoreductase by sulforaphane isothiocyanates?

Isothiocyanates (ITC) are well-known chemopreventive agents extracted from vegetables. This activity results from the activation of human oxidoreductase. In this letter, the uncompetitive activatory mechanism of ITC was investigated using docking and molecular dynamics simulations. This indicates that NAD(P)H:quinone oxidoreductase can efficiently improve enzyme-substrate recognition within the catalytic site if the ITC activator supports the interaction in the uncompetitive binding site.