Spectroscopic characterization,calorimetric study and molecular docking to evaluate the bioconjugation of maltol with hemoglobin

Maltol, a food additive, is extensively used in our daily life. To date, its biological safety is still debated. In this article, binding interaction of maltol with bovine hemoglobin (BHb), an important functional protein, was studied by molecular docking research and spectroscopic and calorimetric measurements. We found that maltol could cause structural changes of BHb. By interacting with Glu 101 (1.27 Å) and Lys 104 (2.49 Å) residues, maltol changed the cavity structure and induced a microenvironment change around tryptophan (Trp) residue. Thermodynamic parameters obtained from isothermal titration calorimetry (ITC) measurement showed that hydrophobic forces were the main forces existing in this system. The association constant of K (8.0 ± 3.4 × 10⁴ M^?1) shows the mild ligand–protein binding for maltol with BHb. The α‐helix amount in BHb increased (59.6–62.6%) with different concentrations of maltol and the intrinsic fluorescence intensity was quenched by maltol, indicating the conformation changes and denaturation of BHb. This work presents the interactions of maltol with BHb at the molecular level and obtains evidence that maltol induces adverse effects to proteins in vitro.     

Studies of the effect of halide ions on the fluorescence of quinine sulfate

The effect of halide ions (Cl^?, Br^? and I^?) on the fluorescence of quinine sulfate in dilute sulfuric acid solution was studied by fluorescence spectra, ultraviolet‐visible (UV‐visible) absorption spectra and fluorescence decay technique. The results exhibited that halide ions with heavier atomic mass could significantly reduce the fluorescence intensity of quinine sulfate, as a result, the order of fluorescence quenching caused by halide ions is Cl^? < Br^? < I^?. Therefore, halide ions with high concentration could seriously quench the fluorescence of quinine sulfate. The UV‐visible absorption spectra and fluorescence decay technique revealed that the fluorescence quenching of quinine sulfate caused by halide ions was attributed to dynamic quenching, static quenching process, self‐quenching fluorescence effect and electronic transfer.     

Prooxidant Action of Maltol: Role of Transition Metals in the Generation of Reactive Oxygen Species and Enhanced Formation of 8-hydroxy-2′-deoxyguanosine Formation in DNA

Maltol (3-hydroxy-2-methyl-4-pyrone) produced reactive oxygen species as a complex with transition metals. Maltol/iron complex inactivated aconitase the most sensitive enzyme to oxidative stress. The inactivation of aconitase was iron-dependent, and prevented by TEMPOL, a scavenger of reactive oxygen species, suggesting that the maltol/iron-mediated generation of superoxide anion is responsible for the inactivation of aconitase. Addition of maltol effectively enhanced the ascorbate/copper-mediated formation of 8-hydroxy-2′-deoxyguanosine in DNA. Oxidation of ascorbic acid by CuSO₄ was effectively stimulated by addition of maltol, and the enhanced oxidation rate was markedly inhibited by the addition of catalase and superoxide dismutase. These results suggest that maltol can stimulate the copper reduction coupled with the oxidation of ascorbate, resulting in the production of superoxide radical which in turn converts to hydrogen peroxide and hydroxyl radical. Cytotoxic effect of maltol can be explained by its prooxidant properties: maltol/transition metal complex generates reactive oxygen species causing the inactivation of aconitase and the production of hydroxyl radical causing the formation of DNA base adduct.     

Evidence of a direct chemical plant defense role for maltol against spruce budworm

This study examines the direct chemical defensive role of maltol, a previously identified secondary metabolite found in balsam fir, Abies balsamea (L.) Mill. (Pinaceae), that was detected during herbivory of spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). Although used extensively in many industries, in addition to being found in multiple plant species, its functional role in plants remains unknown. The objectives of this study were to quantify the amount of free maltol and its potential conjugated form, maltol glucoside, in various foliage age classes and to evaluate whether constitutive foliage levels of maltol have an impact on spruce budworm fitness in maltol supplementation assays. Gas chromatography–mass spectrometry (GC‐MS) analysis of balsam fir foliage showed that maltol is produced in all foliage age classes tested; however, concentrations were significantly higher in older foliage. Liquid chromatography–mass spectrometry–mass spectrometry (LC‐MS‐MS) analysis showed that maltol also exists in balsam fir in its glucosylated form, a unique discovery in conifers. Similar to maltol, maltol glucoside is also present in current and 1‐year‐old balsam fir foliage and in significantly higher concentration in older foliage. We investigated the impact of maltol‐treated diet on spruce budworm fitness. Maltol additions that reflected constitutive foliage concentrations caused a significant reduction in larval development rate and pupal mass, whereas higher concentrations were required to cause significant mortality. These results suggest that maltol may be an important component of a direct defense strategy in balsam fir against spruce budworm herbivory.     

麦芽酚对活性氧损伤人神经瘤细胞的保护作用

以人神经瘤细胞株 (SH SY5Y)为材料 ,使用过氧化氢 (H2 O2 )产生过量活性氧诱导SH SY5Y细胞株进入氧化应激状态 .研究麦芽酚对过量活性氧造成的SH SY5Y细胞株氧化损伤的保护作用 .分析活性氧对细胞膜蛋白和DNA的损伤 ,细胞线粒体功能变化 ,白介素 6 (IL 6 )的表达变化以及细胞核因子κB(NF κB)的激活 .结果显示 ,2mmol L麦芽酚保护细胞 2h后 ,对细胞膜蛋白和DNA的损伤均有明显的保护作用 ,减少了膜蛋白的氧化和细胞DNA片段化的形成 ,细胞线粒体功能损伤减小 ,细胞表达的IL 6减少 ,被激活的NF κB水平同时降低 .结果证明 ,麦芽酚可以有效保护活性氧对神经细胞的氧化损伤 ,维持细胞的正常生理功能     

Subcellular distribution and activities of superoxide dismutase,catalase, glutathione peroxidase,and glutathione reductase in the southern armyworm,Spodoptera eridania

In mid-fifth-instar larvae of the southern armyworm, Spodoptera eridania, the subcellular distribution of four antioxidant enzymes—superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPOX), and glutathione reductase (GR)—were examined. Two-thirds (4.26 units ·mg protein^?1) of the SOD activity was found in the cytosol, and one-thirds (2.13 units ·mg protein^?1) in the mitochondria. CAT activity was unusually high and not restricted to the microsomal fraction where peroxisomes are usually isolated. The activity was distributed as follows: cytosol (163 units) mitochondria (125 units) and microsomes (119 units). Similar to CAT, the subcellular compartmentalization of both GPOX and GR was unusual. No activity was detected in the cytosol, but in mitochondria and microsomes, GR levels were 5.49 and 3.09 units. Although GPOX activity exhibited 14–16-fold enrichment in mitochondria and microsomes, respectively, over the 850g crude homogenate, the level was negligible (mitochondria = 1.4 × 10^?3 units; microsomes = 1.6 × 10^?3 units), indicating that this enzyme is absent. The unusual distribution of CAT has apparently evolved as an evolutionary answer to the absence of GR from the cytosol, and the lack of GPOX activity.     

Effect of Maltol on the Oxidation of DL-DOPA,Dopamine, N-Acetyldopamine (NADA), and Norepinephrine by Mushroom Tyrosinase

Maltol (3-hydroxy-2-methyl-4H-pyran-4-one) appears to inhibit the rate of oxidation of DL-DOPA, dopamine, NADA and epinephrine by tyrosinase when assayed spectropho-tometrically but not when assayed polarographically. Maltol has an effect on the spectrum of product(s) formed when each catecholamine was oxidized by tyrosinase showing that maltol hastens the disappearance of the quinones, possibly by conjugating with them. Indeed, at relatively high concentrations, maltol prevented the conversion of DL-DOPA, dopamine, and norepinephrine to their corresponding melanins via tyrosinase.     

Molecular investigation of the interaction between ionic liquid type gemini surfactant and lysozyme: A spectroscopic and computational approach

Herein, we are reporting the interaction of ionic liquid type gemini surfactant, 1,4‐bis(3‐dodecylimidazolium‐1‐yl) butane bromide ([C₁₂?4‐C₁₂im]Br₂) with lysozyme by using Steady state fluorescence, UV‐visible, Time resolved fluorescence, Fourier transform‐infrared (FT‐IR) spectroscopy techniques in combination with molecular modeling and docking method. The steady state fluorescence spectra suggested that the fluorescence of lysozyme was quenched by [C₁₂?4‐C₁₂im]Br₂ through static quenching mechanism as confirmed by time resolved fluorescence spectroscopy. The binding constant for lysozyme‐[C₁₂?4‐C₁₂im]Br₂ interaction have been measured by UV‐visible spectroscopy and found to be 2.541 × 10⁵M^?1. The FT‐IR results show conformational changes in the secondary structure of lysozyme by the addition of [C₁₂?4‐C₁₂im]Br₂. Moreover, the molecular docking study suggested that hydrogen bonding and hydrophobic interactions play a key role in the protein‐surfactant binding. Additionally, the molecular dynamic simulation results revealed that the lysozyme‐[C₁₂?4‐C₁₂im]Br₂ complex reaches an equilibrium state at around 3 ns. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 406–415, 2015.     

Carbofuran- and cypermethrin-induced histopathological alterations in the liver of Labeo rohita (Hamilton) and its recovery

Alterations in the liver histology of Labeo rohita were examined after exposure to different concentrations of carbofuran (0.06 and 0.15 mg L^?1) and cypermethrin (0.16 and 0.40 μl L^?1) for 28 days. Histological recovery was also studied by maintaining the intoxicated fish in a freshwater system for an additional 28 days. Major damages caused by carbofuran toxicity were diffuse necrosis, cordal disarrangement, individualization of hepatocytes, etc.; significant changes induced by cypermethrin were hyperplasia, disintegration of hepatic mass, focal coagulative necrosis, etc. In both cases, damages were dose‐dependent, with cypermethrin exhibiting more sensitivity than carbofuran. In all cases, recovery was prominent and rate of recovery was faster with carbofuran than when using cypermethrin.     

Maltol inhibits apoptosis of human neuroblastoma cells induced by hydrogen peroxide

To analyze the effect of Maltol on the apoptosis of Human Neuroblastoma Cells (SH-SY5Y) treated by free radical which was generated from Hydrogen Peroxide (H2O2), flow cytometry analysis on Phosphatidylserine (PS) inverting percentage was applied to determine the apoptosis. MTT (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) assay was employed to analyze the cell viability. DNA electrophoresis was used to detect DNA fragmentation. Moreover intracellular calcium of concentration ([Ca2+]i) was measured by fluorescence emission. Flow cytometry analysis on the function of mitochondria and Western blot analysis of NF-kappaB. The results showed that the pretreatment with maltol for 2 hours could prevent the H2O2-induced apoptosis. Maltol could reduce the inverting percentage of PS, DNA fragmentation and [Ca2+]i, and enhance the cellular function of mitochondria. NF-kappaB activated by H2O2 is reduced. The experiments suggest that maltol could effectively inhibit the apoptosis induced by H2O2. As a novel anti-oxidant, maltol is a new promising drug in protecting the neurological cells from the damage by free radical.     

IDENTIFICATION AND CHARACTERIZATION OF THE CATALASE GENE PyCAT FROM THE RED ALGA PYROPIA YEZOENSIS (BANGIALES,RHODOPHYTA)1

Catalase is an antioxidant enzyme that plays a significant role in protection against oxidative stress by reducing hydrogen peroxide. The full‐length catalase cDNA sequence as isolated from expressed sequence tags (ESTs) of Pyropia yezoensis (Ueda) M. S. Hwang et H. G. Choi (PyCAT) through rapid amplification of cDNA ends (RACE) was identified and characterized. It encoded a polypeptide of 529 amino acids, which shared 36%–44% similarity with other known catalase proteins. Phylogenetic analysis revealed that PyCAT was closer to the catalases from plants than from other organisms. The PyCAT mRNA expression was investigated using real‐time PCR to determine life‐cycle‐specific expression and the expression pattern during desiccation. The mRNA expression level in gametophytes was significantly higher than in sporophytes, and the mRNA expression level of PyCAT was significantly up‐regulated during the desiccation process. The recombinant PyCAT protein was purified and analyzed biochemically. The recombinant PyCAT protein exhibited high enzymatic activity (28,000 U·mg^?1) with high thermal stability and a broad pH range. All these results indicate that the PyCAT is a typical member of the plant and algal catalase family and may play a significant role in minimizing the effect of oxidative damage in P. yezoensis during desiccation.     

Interaction of coumarin triazole analogs to serum albumins: Spectroscopic analysis and molecular docking studies

The interaction of triazole substituted 4‐methyl‐7‐hydroxycoumarin derivatives (CUM1‐4) with serum albumin (bovine serum albumin [BSA] and human serum albumin [HSA]) have been studied employing ultraviolet‐visible (UV‐Vis), fluorescence, circular dichroism (CD) spectroscopy, and molecular docking methods at physiological pH 7.4. The fluorescence quenching occurred with increasing concentration of CUMs, and the binding constant of CUM derivatives with BSA and HSA obtained from fluorescence quenching experiment was found to be ~ 10⁴ L mol^?1. CD study showed conformational changes in the secondary structure of serum albumin upon titration of CUMs. The observed experimental results were further validated by theoretical studies involving density functional theory (DFT) and molecular docking.     

Effect of N‐acetylarginine,a metabolite accumulated in hyperargininemia,on parameters of oxidative stress in rats: protective role of vitamins and L‐NAME

In the present investigation, we initially evaluated the in vitro effect of N‐acetylarginine on thiobarbituric acid‐reactive substances (TBA‐RS), total sulfhydryl content and on the activities of antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH‐Px) in the blood, kidney and liver of rats. Results showed that N‐acetylarginine, at a concentration of 5.0 μM, decreased the activity of CAT in erythrocytes, enhanced TBA‐RS in the renal cortex, decreased CAT and SOD activities in the renal medulla and decreased CAT and increased SOD and GSH‐Px activities in the liver of 60‐day‐old rats. Furthermore, we tested the influence of the antioxidants, trolox and ascorbic acid, as well as of the N^ω‐nitro‐L ‐arginine methyl ester (L‐NAME) on the effects elicited by N‐acetylarginine on the parameters tested. Antioxidants and L‐NAME prevented most of the alterations caused by N‐acetylarginine on the oxidative stress parameters evaluated. Data indicate that oxidative stress induction is probably mediated by the generation of NO and/or ONOO^? and other free radicals because L‐NAME and antioxidants prevented the effects caused by N‐acetylarginine in the blood, renal tissues and liver of rats. Our findings lend support to a potential therapeutic strategy for this condition, which may include the use of appropriate antioxidants for ameliorating the damage caused by N‐acetylarginine. Copyright © 2014 John Wiley & Sons, Ltd.     

The binding interaction between cadmium‐based,aqueous‐phase quantum dots with Candida rugosa lipase

As a promising biolabeling biomaterials, quantum dots (QDs) present a great potential. However, the toxicity of QDs to organisms has attracted wide attention. In our research, we introduced an in vitro method to study the molecular mechanisms for the structure and activity alterations of Candida rugosa lipase (CRL) with the binding of 3‐mercaptopropionic acid‐capped CdTe QDs. Multiple spectroscopic methods, isothermal titration calorimetry, and enzyme activity measurements were used in this paper. QDs statically quenched the intrinsic fluorescence of CRL with the quenching constant decreases from 2.46 × 10¹³ to 1.64 × 10¹³ L mol^?1 second^?1 (298 to 310 K). It binds to CRL through hydrophobic force with 1 binding site, unfolding and loosening the skeleton and changed its secondary structure. Rather than aggregating on the surface, it enters the pocket of the CRL to interact with Ser‐209 (2.43 Å) and the residues surrounding Ser‐209, making the catalytic triad more exposed. Furthermore, the activity of CRL was inhibited by approximately 15%. This work demonstrates that 3‐mercaptopropionic acid‐capped CdTe QDs may cause negative effects to CRL and obtains a molecular mechanism on QD‐induced toxicity to proteins in vitro.     

Effects of metalaxyl enantiomers stress on root activity and leaf antioxidant enzyme activities in tobacco seedlings

The objective of this experiment was to study the effects of metalaxyl enantiomers on the activity of roots and antioxidative enzymes in tobacco seedlings. Water culture experiment was conducted to analyze the effects of different concentrations of metalaxyl enantiomers (30 and 10 mg L^?1) on root activity and leaf superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and malondialdehyde (MDA) content of tobacco seedlings. The results showed that metalaxyl significantly inhibited root activity and significantly improved leaf SOD, POD, and CAT activities and MDA content. A better physiological response in tobacco seedlings was observed at 30 mg L^?1 than at 10 mg L^?1 metalaxyl. The stereoselectivity for different enantiomers had no obvious effect on root activity and the leaf POD activity, but it affected significantly the SOD and CAT activities and MDA content. The SOD activity was promoted more by R‐enantiomer than by S‐enantiomer at 30 mg L^?1 metalaxyl, and the same effect was observed on CAT activity from the beginning to the end of the stress period. The MDA content under the stress by R‐enantiomer was higher than that under the stress by S‐enantiomer at 10 mg L^?1 metalaxyl.     

Propolis reduces oxidative stress in l‐NAME‐induced hypertension rats

The inhibition in the synthesis or bioavailability of nitric oxide (NO) has an important role in progress of hypertension. The blocking of nitric oxide synthase activity may cause vasoconstriction with the formation of reactive oxygen species (ROS). Propolis is a resinous substance collected by honey bees from various plants. Propolis has biological and pharmacological properties. The aim of this study was to examine the effect of propolis on catalase (CAT) activity, malondialdehyde (MDA) and NO levels in the testis tissues of hypertensive rats by Nω‐nitro‐l ‐arginine methyl ester (l ‐NAME). Rats have received nitric oxide synthase inhibitor (l ‐NAME, 40 mg kg^?1, intraperitoneally) for 15 days to produce hypertension and propolis (200 mg kg^?1, by gavage) during the last 5 days. MDA level in l ‐NAME‐treated group significantly increased compared with control group (P < 0.01). MDA level of l ‐NAME + propolis‐treated rats significantly reduced (P < 0.01) compared with l ‐NAME‐treated group. CAT activity and NO level significantly reduced (P < 0.01) in l ‐NAME group compared with control group. There were no statistically significant increases in the CAT activity and NO level of the l ‐NAME + propolis group compared with the l ‐NAME‐treated group (P > 0.01). These results suggest that propolis changes CAT activity, NO and MDA levels in testis of l ‐NAME‐treated animals, and so it may modulate the antioxidant system. Copyright © 2013 John Wiley & Sons, Ltd.     

Protective effect of binaphthyl diselenide,a synthetic organoselenium compound,on 2‐nitropropane‐induced hepatotoxicity in rats

Organoselenides have been documented as promising pharmacological agents against a number of diseases associated with oxidative stress. Here we have investigated, for the first time, the potential antioxidant activity of binaphthyl diselenide ((NapSe)₂; 50 mg kg^?1, p.o.) against the 2‐nitropropane (2‐NP)‐induced hepatoxicity in rats, using different end points of toxicity (liver histopathology, plasma aspartate aminotransferase (AST), alanine aminotransferase (ALT) and creatinine). In addition, in view of the association of oxidative stress with 2‐NP exposure, hepatic lipid peroxidation, ascorbic acid levels, δ‐aminolevulinate dehydratase (δ‐ALA‐D) and catalase (CAT) activities were evaluated. 2‐NP caused an increase of AST, ALT and hepatic lipid peroxidation. 2‐NP also caused hepatic histopathological alterations and δ‐ALA‐D inhibition. (NapSe)₂ (50 mg kg^?1) prevented 2‐NP‐induced changes in plasmatic ALT and AST activities and also prevented changes in hepatic histology, δ‐ALA‐D and lipid peroxidation. Results presented here indicate that the protective mechanism of (NapSe)₂ against 2‐NP hepatotoxicity is possibly linked to its antioxidant activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Issue information

The effect of 3‐mercaptopropionic acid (MPA)‐capped CdTe quantum dots (QDs) on lysozyme was systematically investigated by spectroscopic methods, enzyme activity assay, and calorimetry techniques. Results show that the MPA‐capped CdTe QDs binded to lysozyme through van der Walls forces and hydrogen bondings, causing the decrement of α‐helical content (～7%) and increment of β‐sheet content (～11%) of lysozyme. The binding caused static quenching of the fluorescence, while the microenvironment of aromatic amino acid residues did not show any significant alteration. The lysozyme activity was affected by the increasing exposure of QDs, it was inhibited to 53.77% under a 6 × 10^?7 M exposure compared with the control group. This work will provide direct evidence about enzyme toxicity of QDs to lysozyme in vitro .     

The effects of Al(III) speciation on the activity of trypsin

The effects of the different forms of Al(III) on the catalytic activity of the serine protease trypsin were studied. Enzyme activity was measured by BAEE assay in the presence of AlCl(3), Al(III):lactic acid 1:3, Al(III):maltol 1:3 or Al(III):nitrilotriacetic acid (NTA) 1:1 at a nominal Al(III) concentration of 0.01 M, and the ligand alone at pH 7.4 at 25 degrees C. Maltol and NTA caused approximately 30% inhibition, while that for the corresponding Al(III) complex was less than half of this. Al(III) in the form of the chloride or in three equivalents of lactic acid did not influence the activity of the enzyme, probably because most of the Al(III) was precipitated as Al(OH)(3). No direct interaction could be detected between the enzyme and the Al(III) complexes, either by ultrafiltration or by CD spectroscopy. These results strongly suggest that there is no direct involvement of Al(III) in the enzymatic reactions of trypsin.