Steady-state kinetics of combined oxidation of hydroquinone and o-dianisidine by hydrogen peroxide in the presence of horseradish peroxidase

The steady-state kinetics of horseradish peroxidase-catalyzed oxidation of hydroquinone was studied. Hydroquinone was shown to be a rapidly oxidizable substrate of the peroxidase. Values of kcat and Km for this substrate were determined in the pH range 4-7. The oxidation of hydroquinone and o-dianisidine was distinguished when both were present in the reaction mixture. o-Dianisidine was not oxidized until hydroquinone was completely converted. The rate of hydroquinone oxidation by peroxidase in the presence of o-dianisidine was 3-10 times higher than the rate of its individual oxidation. The activator decreased the Km for hydroquinone oxidation.     

Prediction of the three-dimensional structure of aflatoxin of Aspergillus flavus by homology modelling

Aflatoxins are polyketide-derived secondary metabolites produced by Aspergillus spp. The toxic effects of aflatoxins have adverse consequences for human health and agricultural economics. The aflR gene, a regulatory gene for aflatoxin biosynthesis, encodes a protein containing a zinc-finger DNA-binding motif. AFLR-Protein three-dimensional model was generated using Robetta server. The modeled AFLR-Protein was further optimization and validation using Rampage. In the simulations, we monitored the backbone atoms and the C-α-helix of the modeled protein. The low RMSD and the simulation time indicate that, as expected, the 3D structural model of AFLR-protein represents a stable folding conformation. This study paves the way for generating computer molecular models for proteins whose crystal structures are not available and which would aid in detailed molecular mechanism of inhibition of aflatoxin.     

Mapping the amino acid properties of constituent nucleoporins onto the yeast nuclear pore complex

Visualization of molecular structures aids in the understanding of structural and functional roles of biological macromolecules. Macromolecular transport between the cell nucleus and cytoplasm is facilitated by the nuclear pore complex (NPC). The ring structure of the NPC is large and contains several distinct proteins (nucleoporins) which function as a selective gate for the passage of certain molecules into and out of the nucleus. In this note we demonstrate the utility of a python code that allows direct mapping of the physiochemical properties of the constituent nucleoporins on the scaffold of the yeast NPC׳s cytoplasmic view. We expect this tool to be useful for researchers to visualize the NPC based on their physiochemical properties and how it alters when specific mutations are introduced in one or more of the nucleoporins. The code developed using Python is available freely from the authors.     

The Antioxidant System of Wheat Seeds during Germination

The dynamics of peroxidase activity and antioxidant contents in wheat seeds were studied in the course of 24-hour swelling at 5°C (group 1) and 23°C (group 2). Both parameters were 1.5 times higher in seeds of the first group. In the same seeds, peroxidase activity in the endosperm and seed coat increased by factors of 1.5 and 1.8, respectively. Catalytic constants of wheat seed peroxidase were determined in the reactions of o-dianisidine and ascorbic acid peroxidation. In the pH range studied (pH 5–7), K _m proved to change only slightly. In seedlings, an increase in the lipid peroxidation rate was accompanied by an increase in the content of antioxidants. Peroxidase activity increased as the content of antioxidants decreased, and vice versa. Thus, the reciprocal influence of peroxidase and low-molecular antioxidants during seed germination in wheat was revealed.     

Two types of PS II centres as manifested by light saturation of delayed fluorescence from DCMU-treated chloroplasts

Intensity of 2 s delayed fluorescence (DF) as a function of steady-state actinic light intensity was investigated in pea chloroplasts in the presence of 10 M DCMU. The light saturation curve of DF was approximated by a sum of two hyperbolic components which differ by an order of magnitude in the half-saturating incident light intensity. The relative contribution of the amplitudes of the components was practically independent of cation (Na⁺ and Mg²⁺) concentration and a short-term heating of the chloroplasts at 45°C. The component saturating at low incident light intensity was selectively suppressed by 100 M DCMU or by 1 mol g^-1 Chl oleic acid. DF intensity following excitation by a single saturating 15 s flash was equal to the intensity of the component saturating at a low incident light intensity. Upon flash excitation, the maximum steady-state DF level was found to be attained only after a series of saturating flashes. It is concluded that the two components of the DF light saturation curves are related to PS II centres heterogeneity in quantum yield of stabilization of the reduced primary quinone acceptor.Abbreviations DF Delayed fluorescence - L₁- and L₂-components DF components saturating at low and high incident light intensity, respectively - I incident light intensity - L DF intensity - P₆₈₀ reaction centre chlorophyll of PS II - Q_A and Q_B primary and secondary quinone acceptors of PS II, respectively     

Chromosome regions associated with the activity of lipoxygenase in the genome D of <Emphasis Type="Italic">Triticum aestivum</Emphasis> L. under water deficit

Quantitative trait loci (QTLs) associated with the phenotypic expression of the activity of different forms of lipoxygenase (LOX) under water deficit were detected in the chromosomes of the D-genome using intogression lines of common wheat Triticum aestivum L. Chinese Spring (Synthetic 6x). QTL associated with the activity of seed soluble LOX was identified on the short arm of chromosome 4D. The activity of membranebound form of enzyme in the seedlings was mapped to the short arm, while that of a soluble form was on the long arm of chromosome 5D. Two regions responsible for the activity of soluble LOX in the leaves were found on the short arm of chromosome 2D. Three QTLs associated with the activities of chloroplast LOXs were found on the same chromosome: the activity of the soluble form was linked to Xgwm261 and Xgwm539 markers, and the membrane form to Xgdm93 marker. QTLs for the activities of both soluble and membrane-bound LOX in the leaves were identified in the centromeric region of chromosome 7D. The activities of two membrane enzymes in the leaves were linked to Xgdm130 marker on the short arm of this chromosome. Loci associated with the activity of different LOX forms colocalized with QTLs for the shoot mass, gas exchange parameters, chlorophyll fluorescence, content of photosynthetic pigments, and grain productivity of wheat. A correlation between these parameters and the LOX activity was detected and it was shown that various forms of the enzyme were differentially involved in the adaptation of wheat plants to water deficit. The current paper discusses their presumed physiological role.     

Mechanism of combined oxidation of ascorbic acid and hydroquinone in the presence of horseradish peroxidase]

A steady-state kinetics of peroxidase cooxidation of ascorbic acid and hydroquinone catalyzed by horseradish peroxidase was studied. Ascorbic acid and hydroquinone were shown to be oxidized successively, and hydroquinone promoted the oxidation of ascorbic acid. Excess ascorbic acid inhibited peroxidase in the cooxidation of the substrates at pH 5-7. The values of catalytic constants, (kcat, K(m), and Ka) were determined. A possible activation mechanism of the peroxidation of ascorbic acid in the presence of hydroquinone was suggested, and its biological significance was considered.