Search

During development apples may become infected with mycotoxin-producing fungi without showing surface symptoms at fruit maturity. Cores from five apple cultivars: Ambrosia, Honey Crisp, Golden Delicious, Red Delicious and McIntosh, were aseptically removed from surface sterilized fruit and incubated at 25 °C. The cores were screened for the presence of fungal mycelium and associated mycotoxins. The average percentage of cores with fungal presence was 53.3–58.0%. Twenty five fungal species were identified by sequencing internal transcribed spacers (ITS) of 18S rDNA. The fungi mainly belonged to Alternaria, Penicillium, Aspergillus, Fusarium and Trichoderma species. Fungal pure cultures were inoculated into the apple matrix and incubated for 14 days. Liquid chromatography-mass spectroscopy demonstrated that the isolated fungi had the capacity to produce mycotoxins patulin, alternariol, tentoxin, ochratoxin A and T2-toxin. In addition, mycotoxin-specific genes and/or their transcripts were detected in some of the fungal isolates, but their corresponding mycotoxins were not detected in all isolates containing the genes.

Beauvericin (BEA) is a bioactive compound produced by the secondary metabolism of several Fusarium species and known to have various biological activities. This study investigated the degradation of the minor Fusarium mycotoxin BEA present at the concentration of 5 mg/kg in barley and wheat flour during beer and bread making. The influence of the making processes and of the formation of degradation products of BEA were evaluated during the beer and bread making. The concentration of BEA and its evolution during the production processes were determined with the technique of the liquid chromatography tandem mass spectrometry in tandem (LC-MS/MS), whereas the formation of the BEA degradation products was determined with the technique of the LC-MS coupled to a linear ion trap (LC-MS-LIT). The degradation of BEA during beer making ranged from 23 to 82%. During bread making, BEA reduction ranged from 75 to 95%. The highest degradation activity of BEA for both beer and bread was evidenced during the heat and fermentation processes. Also two degradation products formed during these processes were identified.

Beauvericin (BEA) is a cyclic depsipeptide with antibiotic and insecticidal effects. It was discovered for the first time from the fungus Beauveria bassiana , but more significantly, is produced by several Fusarium strains, and considered a contaminant of several cereals like corn, wheat and barley. This study investigated the degradation of BEA by intracellular raw enzymes of four strains of Saccharomyces cerevisiae , named LO9, YE5, A34, and A17. The BEA at 25 mg/kg in a model solution and in corn flour was co-incubated with the raw enzymes from the four yeast strains, respectively. The reduction of BEA was evaluated using liquid chromatography coupled to a diode array detector (LC–DAD); the products formed during the co-incubation were determined by liquid chromatography coupled to mass spectrometry-linear ion trap (LC–MS-LIT). In model solution BEA reduction ranged from 83 to 100%. In corn flour treated with the intracellular raw enzymes, the BEA degradation was from 66 to 91%. A product resulted from the BEA degradation was identified.

The crystal structure of a high temperature (HT) Al3Co phase, which is isostructural to the Al13Os4 phase, was determined by means of single-crystal X-ray diffraction: space group C2/m (No. 12), a = 16.989(4) A, b = 4.098(1) A, c = 7.478(2) A, β = 115.812(5)°, V = 467.9(2) A3, Dc = 3.998 g cm−3, λ(Mo Kα) = 0.71073 A, F(0 0 0) = 532, Mr = 140.81, μ = 8.044 mm−1, Z = 8, R = 0.068 for 373 reflections with I > 2 σ(I), w R 2 = 0.182 for 522 unique reflections, Np = 59, S = 1.037. The HT-Al3Co phase is a crystalline approximant of decagonal quasicrystals. Crystalline phases with the composition among Al11Co4–Al13Co4 have been briefly reviewed.

Local tissue concentrations of glucocorticoids are modulated by the enzyme 11 β -hydroxysteroid dehydrogenase which interconverts cortisol and the inactive glucocorticoid cortisone in man, and corticosterone and 11-dehydrocorticosterone in rodents. The type I isoform (11 β -HSD1) is a bidirectional enzyme but acts predominantly as a oxidoreductase to form the active glucocorticoids cortisol or corticosterone, while the type II enzyme (11 β -HSD2) acts unidirectionally producing inactive 11-keto metabolites. There are no known clinical conditions associated with 11 β -HSD1 deficiency, but gene deletion experiments in the mouse indicate that this enzyme is important both for the maintenance of normal serum glucocorticoid levels, and in the activation of key hepatic gluconeogenic enzymes. Other important sites of action include omental fat, the ovary, brain and vasculature. Congenital defects in the 11 β -HSD2 enzyme have been shown to account for the syndrome of apparent mineralocorticoid excess (AME), a low renin severe form of hypertension resulting from the overstimulation of the non-selective mineralocorticoid receptor by cortisol in the distal tubule of the kidney. Inactivation of the 11 β -HSD2 gene in mice results in a phenotype with similar features to AME. In addition, these mice show high neonatal mortality associated with marked colonic distention, and remarkable hypertrophy and hyperplasia of the distal tubule epithelia. 11 β -HSD2 also plays an important role in decreasing the exposure of the fetus to the high levels of maternal glucocorticoids. Recent work suggests a role for 11 β -HSD2 in non-mineralocorticoid target tissues where it would modulate glucocorticoid access to the glucocorticoid receptor, in invasive breast cancer and as a mechanism providing ligand for the putative 11-dehydrocorticosterone receptor. While previous homologies between members of the SCAD superfamily have been of the order of 20–30% phylogenetic analysis of a new branch of retinol dehydrogenases indicates identities of >60% and overlapping substrate specificities. The availability of crystal structures of family members has allowed the mapping of conserved 11 β -HSD domains A–D to a cleft in the protein structure (cofactor binding domain), two parallel β -sheets, and an α -helix (active site), respectively.

Structure of the AlRhCu decagonal quasicrystal has been studied by high-resolution electron microscopy. The high-resolution structure image shows an aperiodic tiling composed of three kinds of subunits, namely flattened hexagon, crown and five star. Therefore, a structural model of the AlRhCu decagonal quasicrystal has been constructed in a unit-cell approach, in which the atom arrangements in the subunits have been proposed. It is known that the phase has two layers in a period of 0.4 nm along the unique tenfold axis according to the previous study by electron diffraction method. The ideal model of the AlRhCu decagonal quasicrystal is proposed as periodic stacking of the layers with quasiperiodic tessellation of the three kinds of subunits, in each layer the two-colour Penrose tiling is obtained if different atom decorations for the same shape subunits are distinguished by white and black colours. Calculated images reproduces well the contrast features of the observed images, which means that the present model is basically correct. Structural relationship between the AlRhCu decagonal quasicrystal and the previously reported AlNiCo decagonal quasicrystal, which has also a period of 0.4 nm, has also been discussed.

The 11beta-hydroxysteroid dehydrogenase type II enzyme (11betaHSD2) endows specificity on the mineralocorticoid receptor by metabolising glucocorticoids. Sequence comparisons with other microsomal proteins showed the strongly preferred topology of a lumenal pentapeptide followed by three transmembrane helices with residues beyond Ala73 on the cytoplasmic side of the membrane, suggesting that 11betaHSD2 is anchored to the endoplasmic reticulum by the N-terminal region. However, deletion of the N-terminus (11betaHSD2 deltaN) and expression of the construct in mammalian cells showed that the enzyme remained bound to the microsomal fraction, indicating that other regions are also involved in membrane anchoring. Crosslinking studies and nonreducing SDS-PAGE demonstrated that 11betaHSD2 is a non-covalently linked dimer. Deletion of the non-conserved C-terminal region (11betaHSD2 deltaC) resulted in an enzyme with a Km of 215 nM for cortisol in whole cell assays, while 11betaHSD2 and 11betaHSD2 deltaN displayed a Km of 62 and 74 nM, respectively. In homogenates 11betaHSD2 and 11betaHSD2 deltaC displayed maximal activity at 140 mM NaCl or KCl, but showed a marked decrease in enzyme activity with increasing salt. 11BetaHSD2 was more stable than 11betaHSD2 deltaC in the presence of NaSCN, suggesting that the C-terminal region plays a role in enzyme stability. There was no detectable activity in homogenates containing 11betaHSD2 deltaN, while 11betaHSD2 deltaC and 11betaHSD2 displayed a Km of 135 and 46 nM, respectively. Although 11betaHSD2 is conventionally considered a unidirectional dehydrogenase all constructs converted 11-dehydrodexamethasone to dexamethasone in whole cell assays, providing an explanation for the potency of the synthetic glucocorticoid in the face of a powerful inactivator of natural glucocorticoids.

The 11 beta-hydroxysteroid dehydrogenase type II enzyme (11 beta HSD2) converts cortisol to cortisone, allowing the non-selective mineralocorticoid receptor to bind aldosterone. When the activity of this enzyme is compromised, as occurs in licorice intoxication or in the congenital syndrome of apparent mineralocorticoid excess (AME), there is marked sodium retention, hypokalemia, and hypertension. The first proof that this enzyme was defective in AME came from the identification of the R337C mutation in a number of siblings with the syndrome. Subsequent expression studies showed that the mutant had a Km one order of magnitude higher than the wild-type enzyme while in the cell-free system it was without detectable activity. In the present work we have extended our studies on this mutant and provide evidence that the mutant protein may also partially inhibit the wild-type enzyme in heterozygotes. Furthermore, experiments incorporating the protein synthesis inhibitor cycloheximide show that the mutant enzyme is less stable than the wild-type activity in intact cells. These results suggest that mutations in the 11 beta HSD2 enzyme may have multiple consequences for the mineralocorticoid target cell.