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Phenolic Substrates (phenolic + substrate)

Distribution by Scientific Domains

Chemistry	57%
Life Sciences	42%

Selected Abstracts

Modified Microperoxidases Exhibit Different Reactivity Towards Phenolic Substrates

CHEMBIOCHEM, Issue 12 2004
Corrado Dallacosta Dr.
Abstract The reactivity of several microperoxidase derivatives with different distal-site environments has been studied. The distal-site environments of these heme peptides include a positively charged one, an uncharged environment, two bulky and doubly or triply positively charged ones, and one containing aromatic apolar residues. The reactivity in the catalytic oxidation of two representative phenols, carrying opposite charges, by hydrogen peroxide has been investigated. This allows the determination of the binding constants and of the electron-transfer rate from the phenol to the catalyst in the substrate/microperoxidase complex. The electron-transfer rates scarcely depend on the redox and charge properties of the phenol, but depend strongly on the microperoxidase. Information on the disposition of the substrate in the adducts with the microperoxidases has been obtained through determination of the paramagnetic contribution to the1H NMR relaxation rates of the protons of the bound substrates. The data show that the electron-transfer rate drops when the substrate binds too far away from the iron and that the phenols bind to microperoxidases at similar distances to those observed with peroxidases. While the reaction rate of microperoxidases with peroxide is significantly smaller than that of the enzymes, the efficiency in the one-electron oxidation of phenolic substrates is almost comparable. Interestingly, the oxyferryl form of the triply positively charged microperoxidases shows a reactivity larger than that exhibited by horseradish peroxidase. [source]

Carbon Ceramic Electrodes Modified with Laccase from Trametes hirsuta: Fabrication, Characterization and Their Use for Phenolic Compounds Detection

ELECTROANALYSIS, Issue 9 2007
Behzad Haghighi
Abstract Fungal laccase (Lc) from the basidiomycete Trametes hirsuta was immobilized on top of a carbon ceramic electrode using physical absorption. Direct, unmediated heterogeneous electron transfer between Lc and the carbon ceramic electrode (CCE) under aerobic conditions was shown. The bioelectrocatalytic reduction of oxygen on Lc-CCE started at about 430,mV vs. Ag|AgCl|KClsat at pH,3.5 and moved with about 57,mV in the cathodic region per pH unit. The Lc-modified CCE was then used as a biosensing detection element in a single line flow injection system for the amperometric determination of a variety of phenolic substrates of the enzyme. The experimental conditions were studied and optimized for catechol serving as a model compound. Statistical aspects were applied and the sensor characteristics and Michaelis-Menten constants of the investigated phenolic compounds were calculated and compared with those obtained for solid graphite electrodes modified with Trametes hirsuta laccase. The results showed that the CCE based biosensor in comparison with the solid graphite based biosensor offers a lower detection limit, a wider linear dynamic range, and excellent operational stability with no sensor passivation, indicating that the sol,gel lattice improves the electrochemical behavior of the biosensor. [source]

Transcript and activity levels of different Pleurotus ostreatus peroxidases are differentially affected by Mn2+

ENVIRONMENTAL MICROBIOLOGY, Issue 5 2001
Roni Cohen
The white-rot fungus Pleurotus ostreatus produces both manganese-dependent peroxidase (MnP) and versatile peroxidase (VP) in non-manganese-amended peptone medium (PM). We studied the effect of Mn2+ supplementation on MnPs and VPs in P. ostreatus by analysing the enzymatic and transcript abundance profiles of the peroxidases, as well as the lignin mineralization rate. The fungus was grown in PM under solid-state conditions using perlite as an inert solid support. Mn2+ amendment resulted in a 1.7-fold increase in [14C]-lignin mineralization relative to unamended medium. Anion-exchange chromatography was used to resolve the fungal peroxidase's enzymatic activity profile. Five peaks (P1,P5) of VP and one peak (P6) of MnP activity were detected in unamended medium. In Mn2+ -amended medium, a reduction in the activity of the VPs was observed. On the other hand, a sharp increase in the MnP activity level of peak P6 was detected. The P6 isoenzyme was purified and showed manganese-dependent peroxidation of phenolic substrates. Internal sequence analysis of the purified enzyme revealed 100% identity with the deduced amino acid sequence of P. ostreatus MnP3 (GenBank AB016519). The effect of Mn2+ on the relative abundance of gene transcripts of three VPs and one MnP from P. ostreatus was monitored using reverse transcription,polymerase chain reaction (RT,PCR) with oligonucleotide primer sets synthesized on the basis of non-conserved sequences of the different peroxidases. The reduction in VP gene transcript abundance and the increase in mnp3 transcript level were collinear with the changes observed in the enzyme activity profiles. These results indicate that the activity of peroxidases is regulated at the transcriptional level. We suggest that the expression of MnP and VP may be differentially regulated by the presence of Mn2+. [source]

Inactivation of Escherichia coli and Shigella in acidic fruit and vegetable juices by peroxidase systems

JOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2006
I. Van Opstal
Abstract Aims:, To study the bactericidal properties of the lactoperoxidase (LPER)-thiocyanate and soybean peroxidase (SBP)-thiocyanate systems at low pH, their efficiency for inactivation of Escherichia coli and Shigella in acidic fruit and vegetable juices, their effect on colour stability of the juices and interaction with ascorbic acid. Methods and Results:, Three-strain cocktails of E. coli and Shigella spp. in selected juices were supplemented with the LPER or SBP system. Within 24 h at 20°C, the LPER system inactivated both cocktails by ,5 log10 units in apple, 2,5 log10 units in orange and ,1 log10 unit in tomato juices. In the presence of SBP, browning was significant in apple juice and white grape juice, slight in pink grape juice and absent in orange or tomato juice. Ascorbic acid protected E. coli and Shigella against inactivation by the LPER system, and peroxidase systems significantly reduced the ascorbic acid content of juices. Conclusions:, Our results suggest a different specificity of LPER and SBP for SCN,, phenolic substrates of browning and ascorbic acid in acidic juices. The LPER system appeared a more appropriate candidate than the SBP system for biopreservation of juices. Significance and Impact of the Study:, This work may open perspectives towards the development of LPER or other peroxidases as biopreservatives in acidic foods. [source]

Browning Prevention by Ascorbic Acid and 4-Hexylresorcinol: Different Mechanisms of Action on Polyphenol Oxidase in the Presence and in the Absence of Substrates

JOURNAL OF FOOD SCIENCE, Issue 9 2007
E. Arias
ABSTRACT:, We have investigated the mechanism of action of 4-hexylresorcinol (4-HR) and ascorbic acid (AA) on the polyphenol oxidase (PPO) catalyzed oxidation of phenolic substrates. Incubation of PPO with 4-HR diminishes strongly PPO activity. This effect can be erroneously interpreted, due to the high affinity of 4-HR for PPO, as irreversible inactivation of PPO. However, PPO activity can be recovered by dialysis after incubation with 4-HR. 4-hexylresorcinol is a canonical enzyme inhibitor that binds preferentially to the oxy form of PPO. It is a mixed-type inhibitor, because it influences both apparent Vmax (1.26 compared with 0.4 units in the absence and presence of 4-HR, respectively) and Km values (0.28 mM compared with 0.97 mM in the absence and in the presence of 4-HR, respectively) of PPO. AA can prevent browning by 2 different mechanisms: In the absence of PPO substrates it inactivates PPO irreversibly, probably through binding to its active site, preferentially in its oxy form. In the presence of PPO substrates, AA reduces PPO oxidized reaction products, which results in a lag phase when measuring PPO activity by monitoring dark product formation but not when monitoring O2 consumption. The simultaneous use of both 4-HR and AA on PPO results in additive prevention of browning. [source]

Optimization of catechol production by membrane-immobilized polyphenol oxidase: A modeling approach

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2003
A. Boshoff
Abstract Although previous research has focused on phenol removal efficiencies using polyphenol oxidase in nonimmobilized and immobilized forms, there has been little consideration of the use of polyphenol oxidase in a biotransformation system for the production of catechols. In this study, polyphenol oxidase was successfully immobilized on various synthetic membranes and used to convert phenolic substrates to catechol products. A neural network model was developed and used to model the rates of substrate utilization and catechol production for both nonimmobilized and immobilized polyphenol oxidase. The results indicate that the biotransformation of the phenols to their corresponding catechols was strongly influenced by the immobilization support, resulting in differing yields of catechols. Hydrophilic membranes were found to be the most suitable immobilization supports for catechol production. The successful biocatalytic production of 3-methylcatechol, 4-methylcatechol, catechol, and 4-chlorocatechol is demonstrated. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 1,7, 2003. [source]