Inhibition of Peroxidase-Catalyzed Oxidation of Aromatic Amines by Substituted Phenols

Peroxidase-catalyzed oxidation of o-phenylene diamine (OPD) was competitively inhibited by trimethylhydroquinone (TMHQ), 4-tert-butylpyrocatechol (InH5), and 4,6-di-tert-butyl-3-sulfanyl-1,2-dihydroxybenzene (InH6). InH6 was the most efficient inhibitor (K _i = 11 M at 20°C in 0.015 M phosphate–citrate buffer, pH 6.0). The effects of InH5 and InH6 were not preceded by periods of induction of OPD oxidation products (contrary to TMHQ). Peroxidase-catalyzed oxidation of tetramethylbenzidine (TMB) was noncompetitively inhibited by InH6 and 3-(2-hydroxyethylthio)-4,6-di-tert-butylpyrocatechol (InH4), whereas o-aminophenol acted as a mixed-type inhibitor. The effects of all three inhibitors were preceded by an induction period, during which TMB oxidation products were formed. Again, InH6 was the most efficient inhibitor (K _i = 16 M at 20°C in 0.015 M phosphate–citrate buffer supplemented with 5% ethanol, pH 6.0). Judging by the characteristics of the inhibitors taken in aggregate, it is advisable to use the pairs OPD–InH5 and OPD–InH6 in systems for testing the total antioxidant activity of human biological fluids.     

Quinones as free-radical fragmentation inhibitors in biologically important molecules

Effects of a number of quinones and diphenols of various structures on free-radical fragmentation processes taking place in alpha-diols, glycerol, 2-aminoethanol, glycero-1-phosphate, ethylene glycol monobutyrate, maltose, and some lipids were investigated. Quinone additions have been found to change the direction of free-radical transformations of the compounds cited above by inhibiting formation of the respective fragmentation products owing to oxidation of radicals of the starting compounds. The results obtained and literature data available allow a suggestion to be made that the system quinone/diphenol is able to not only deactivate or generate such active species as O2.- but also control the realization probability of free-radical processes of peroxidation and fragmentation in biologically important molecules.     

Reactions of arylamine and aminophenol derivatives, and riboflavin with organic radicals

Based on product yield data on radiolysis of hexane, ethanol and 3 M aqueous ethylene glycol solutions, the ability of a number of arylamine, aminophenol and quinonimine derivatives to affect processes involving peroxyl, alkyl or alpha-hydroxyalkyl radicals was assessed. It has been shown that the introduction of a hydroxyl group into aromatic amine structure enhances its antioxidant performance and makes it significantly more reactive with respect to carbon-centered organic radicals. Replacement of the hydrogen atom of a hydroxyl group by a methyl group decreases the anti-radical activity of aminophenols drastically. Compounds containing (or capable of forming) a quinonimine moiety interact with alkyl or alpha-hydroxyalkyl radicals most effectively, suppressing recombination and fragmentation reactions of the latter. In the sequence: aromatic amines--aminophenols--quinonimines, a trend towards enhancement of the ability of the compounds studied to react with carbon-centered radicals was noted. Also, this study presents for the first time evidence of riboflavin reactivity with respect to organic radicals.     

Effects of Phenolic Compounds on Reactions Involving Various Organic Radicals

Investigation of effects produced by 26 various phenol and diphenol derivatives, including industrial and natural antioxidants (ionol, bis-phenol 2246, α-tocopherol), on final product yields of radiation-induced free-radical processes involving peroxyl, alkyl, α-hydroxyalkyl and α,β-dihydroxyalkyl radicals has been performed. Ionol and bis-phenol 2246 have been shown to be more effective than α-tocopherol or diphenol derivatives in suppressing hydrocarbon oxidation processes. At the same time, α-tocopherol and its water-soluble analogues, as well as diphenol-based substances, are more effective than phenol derivatives in regulating various homolytic processes involving carbon-centered radicals. This fact can be accounted for by taking into consideration the contribution to formation of the final product set and the respective yields made by semiquinone radicals and compounds with quinoid structure arising in the course of homolytic transformations in systems containing diphenol derivatives.     

Quantitative Trait Locus (QTL) meta-analysis and comparative genomics for candidate gene prediction in perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.)

Background

In crop species, QTL analysis is commonly used for identification of factors contributing to variation of agronomically important traits. As an important pasture species, a large number of QTLs have been reported for perennial ryegrass based on analysis of biparental mapping populations. Further characterisation of those QTLs is, however, essential for utilisation in varietal improvement programs.

Results

A bibliographic survey of perennial ryegrass trait-dissection studies identified a total of 560 QTLs from previously published papers, of which 189, 270 and 101 were classified as morphology-, physiology- and resistance/tolerance-related loci, respectively. The collected dataset permitted a subsequent meta-QTL study and implementation of a cross-species candidate gene identification approach. A meta-QTL analysis based on use of the BioMercator software was performed to identify two consensus regions for pathogen resistance traits. Genes that are candidates for causal polymorphism underpinning perennial ryegrass QTLs were identified through in silico comparative mapping using rice databases, and 7 genes were assigned to the p150/112 reference map. Markers linked to the Lp DGL1, Lp Ph1 and Lp PIPK1 genes were located close to plant size, leaf extension time and heading date-related QTLs, respectively, suggesting that these genes may be functionally associated with important agronomic traits in perennial ryegrass.

Conclusions

Functional markers are valuable for QTL meta-analysis and comparative genomics. Enrichment of such genetic markers may permit further detailed characterisation of QTLs. The outcomes of QTL meta-analysis and comparative genomics studies may be useful for accelerated development of novel perennial ryegrass cultivars with desirable traits.

     

Antioxidant activity of hydroxy derivatives of coumarin

The inhibition efficiency (antioxidant activity) of hydroxy derivatives of coumarin, such as esculetin, dicumarol, and fraxetin, was studied in the methemalbumin-H2O2-tetramethylbenzidine (TMB) pseudoperoxidase system at 20 degrees C in a buffered physiological solution (pH 7.4) containing 6% DMF and 0.25% DMSO. The inhibitor's efficiency was quantitatively characterized by the inhibition constants (K(i), microM) and the inhibition degree (%). The K(i) values for esculetin, dicumarol, and fraxetin were 9.5, 15, and 26 microM, respectively. Esculetin and fraxetin inhibited pseudoperoxidase oxidation of TMB in a noncompetitive manner; dicumarol, in a mixed manner. The inhibiting activity ofesculetin in peroxidase-catalyzed TMB oxidation at pH 6.4 is characterized by a K(i) value equal to 1.15 microM, and the inhibition process is competitive. Esculetin was found to be the most effective antioxidant of plant origin among all derivatives previously studied in model biochemical systems.     

Effect of lysophosphatidylcholine on the radiation-induced lipid peroxidation in liposomes

The effect of lysophosphatidylcholine (LPC) on the lipid peroxidation process (LPO) in liposomes of rat liver phosphatidylcholine initiated by irradiation of 137Cs source was studied. The formation of diene conjugates (DC) is shown to increase dramatically on incorporation of more than 10% LPC into liposomes. The dependence of DC proportion on the irradiation dose is practically linear in the range of 0 to 5 kGy. The DC concentration in the liposomes without LPC grows at least to dose of 3.3 kGy and is unchanged on further irradiation. The malonic dialdehide accumulation follows the similar dependence. The LPC effect is neutralized by the incorporation of cholesterol into liposomes. The product of free radical fragmentation of LPC, palmitoxyacetone, practically has no influence on the DC concentration. The reasons of LPC effect on the irradiation initiated LPO in liposomes is discussed.     

Free-radical fragmentation of galactocerebrosides: a MALDI-TOF mass spectrometry study

Analysis of final products of radiation-induced transformations of galactocerebrosides (GalCer) in aqueous dispersions has been performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and its combination of thin-layer chromatography (TLC). Ceramides were found to be the main products of GalCer gamma-radiolysis. From experimental results obtained in this study, as well as from the data available in the literature, an inference is made that the formation of ceramides occurs owing to fragmentation of radicals with an unpaired electron of the C2 atom of the carbohydrate moiety, formed from the starting compounds.     

Inhibition of peroxidase-catalyzed oxidation of 3,3′,5,5′-tetramethylbenzidine by aminophenols

Peroxidase-catalyzed oxidation of 3,3,5,5-tetramethylbenzidine (TMB) was inhibited by o-aminophenol (AP), 2-amino-4-tert-butylphenol (ATBP), 2-amino-4,6-di-tert-butylphenol (ADTBP), and 4-tert-butylpyrocatechol (TBP). Inhibitors were characterized by inhibition constant K _i and stoichiometric coefficient f, the number of radicals terminated by one inhibitor molecule. The most efficient inhibitor is ADTBP characterized by K _i = 36 µM in 0.015 M phosphate citrate buffer, pH 6.0, at 20°C. According to their antiradical efficiency, the studied inhibitors can be arranged as follows: ADTBP > ATBP > AP > TBP. The role of the NH₂ group in the inhibitory capacity of aminophenols is discussed. Using gas-liquid chromatography, kinetics of consumption of the initial components and accumulation of the reaction products on peroxidase-catalyzed oxidation of the TMB-TBP pair was studied; the data clarify the stages of a complex process of co-oxidation of amines and phenols.Translated from Biokhimiya, Vol. 70, No. 3, 2005, pp. 397–405.Original Russian Text Copyright © 2005 by Naumchik, Karasyova, Metelitza, Edimecheva, Sorokin, Shadyro.