Participation of Low Molecular Weight Electron Carriers in Oxidative Protein Folding

Oxidative protein folding is mediated by a proteinaceous electron relay system, in which the concerted action of protein disulfide isomerase and Ero1 delivers the electrons from thiol groups to the final acceptor. Oxygen appears to be the final oxidant in aerobic living organisms, although the existence of alternative electron acceptors, e.g. fumarate or nitrate, cannot be excluded. Whilst the protein components of the system are well-known, less attention has been turned to the role of low molecular weight electron carriers in the process. The function of ascorbate, tocopherol and vitamin K has been raised recently. In vitro and in vivo evidence suggests that these redox-active compounds can contribute to the functioning of oxidative folding. This review focuses on the participation of small molecular weight redox compounds in oxidative protein folding.     

Oxidative responses in soybean foliage to herbivory by bean leaf beetle and three-cornered alfalfa hopper

Variation in induced responses in soybean is shown to be dependent, in part, upon herbivore species. Herbivory by the phloem-feeding three-cornered alfalfa hopper caused increases in the activities of several oxidative enzymes including lipoxygenases, peroxidases, ascorbate oxidase, and polyphenol oxidase. Bean leaf beetle defoliation caused increased lipoxygenase activity, but had little effect upon peroxidase, polyphenol oxidase, ascorbate oxidase, or trypsin inhibitor levels in either field or greenhouse studies. In one field experiment, prior herbivory by the bean leaf beetle subsequently reduced the suitability of foliage to the corn earwormHelicoverpa zea. The contribution of these findings to emerging theories of insect-plant interactions is discussed.     

Chemical decolorization of the azo dye CI Reactive Orange 96 by various organic/inorganic compounds

Batch experiments were performed to investigate the possibility and kinetics of chemical decolorization of the reactive mono‐azo dye CI Reactive Orange 96 (RO 96) with various compounds such as cysteine, ascorbate, Ti(III)‐citrate, Fe(II)‐sulfate, and yeast extract. Cysteine and ascorbate (10 mmol dm^?3 respectively) decolorized RO 96 (0.19 mmol dm^?3) in the absence of oxygen. Increasing the concentration of either reductant (to 20 or 38 mmol dm^?3) enhanced the decolorization rate, showing first‐order kinetics with respect to both the concentration of the dye and of cysteine or ascorbate. The rate constants, k, for cysteine and ascorbate were 0.0003 and 0.0010 dm³mmol^?1 h^?1 respectively at pH 7.1 and 33 °C. Ti(III)‐citrate (10 mmol dm^?3) decolorized RO 96 (0.20 mmol dm^?3) within 5 min, independent of the presence of oxygen. Fe(II)‐sulfate was not effective in the decolorization of RO 96 at pH 8, whereas a rapid decolorization occurred at pH 12. This study suggests that a variety of abiotic processes may be involved in decolorization under anaerobic conditions. © 2002 Society of Chemical Industry     

Tetrahexyldecyl Ascorbate (THDC) Degrades Rapidly under Oxidative Stress but Can Be Stabilized by Acetyl Zingerone to Enhance Collagen Production and Antioxidant Effects

Tetrahexyldecyl Ascorbate (THDC) is an L-ascorbic acid precursor with improved stability and ability to penetrate the epidermis. The stability and transdermal penetration of THDC, however, may be compromised by the oxidant-rich environment of human skin. In this study, we show that THDC is a poor antioxidant that degrades rapidly when exposed to singlet oxygen. This degradation, however, was prevented by combination with acetyl zingerone (AZ) as a stabilizing antioxidant. As a standalone ingredient, THDC led to unexpected activation of type I interferon signaling, but this pro-inflammatory effect was blunted in the presence of AZ. Moreover, the combination of THDC and AZ increased expression of genes associated with phospholipid homeostasis and keratinocyte differentiation, along with repression of MMP1 and MMP7 expression, inhibition of MMP enzyme activity, and increased production of collagen proteins by dermal fibroblasts. Lastly, whereas THDC alone reduced viability of keratinocytes exposed to oxidative stress, this effect was completely abrogated by the addition of AZ to THDC. These results show that AZ is an effective antioxidant stabilizer of THDC and that combination of these products may improve ascorbic acid delivery. This provides a step towards reaching the full potential of ascorbate as an active ingredient in topical preparations.     

银杏叶提取液结合异抗坏血酸钠对鲜切砀山梨贮藏品质的影响

目的:研究银杏叶提取液结合异抗坏血酸钠对鲜切梨的保鲜效果。方法:以鲜切砀山梨为材料,探究总黄酮含量分别为0.25(处理1)、0.50(处理2)、0.75 mg/m L(处理3)的银杏叶提取液结合1%的异抗坏血酸钠(D-sodium ascorbate,D-VCNa)溶液对鲜切砀山梨在4℃条件下贮藏品质的影响。采用SPSS软件分析了贮藏期间鲜切梨的呼吸强度、质量损失率、色差、VC含量、硬度、可溶性固形物含量(soluble solid content,SSC)、过氧化物酶(peroxidase,POD)活力、相对电导率及pH值的变化等。结果:不同质量浓度黄酮的银杏叶提取液结合D-VCNa溶液都可以在不同程度上减缓鲜切梨的呼吸强度、质量损失率、色差的增加,减缓VC含量、硬度、SSC的下降速率,延迟褐变发生、POD活力高峰的出现时间,抑制果实pH值和相对电导率的上升。结论:银杏叶提取液结合D-VCNa对鲜切砀山梨的贮藏品质有一定的保鲜作用,其中以总黄酮含量为0.50 mg/m L银杏叶提取液结合1%的D-VCNa溶液处理的鲜切梨保鲜效果最好。     

6个不同品系地木耳抗氧化酶活性比较研究

目的：通过对6个不同品系地木耳抗氧化酶活性的比较和分析,筛选抗逆性较高的品系。方法：采用紫外分光光度法测定过氧化氢酶(CAT),采用分光光度法测定抗坏血酸过氧化物酶(APX),采用DTNB染色法测定谷胱甘肽过氧化物酶(GSH-PX)。结果：山西宁武荷叶坪品系CAT活性最大,且与其他品系之间存在显著差异(P＜0.05);山西宁武秋千沟品系GSH-PX、APX活性均明显大于其他品系(P＜0.05)。结论：从抗氧化酶体系来看,秋千沟品系的抗逆性优于其他品系抗逆性。     

Antioxidant Systems from Pepper (Capsicum annuum L.): Involvement in the Response to Temperature Changes in Ripe Fruits

Sweet pepper is susceptible to changes in the environmental conditions, especially temperatures below 15 °C. In this work, two sets of pepper fruits (Capsicum annuum L.) which underwent distinct temperature profiles in planta were investigated. Accordingly, two harvesting times corresponding to each set were established: Harvest 1, whose fruits developed and ripened at 14.9 °C as average temperature; and Harvest 2, with average temperature of 12.4 °C. The oxidative metabolism was analyzed in all fruits. Although total ascorbate content did not vary between Harvests, a shift from the reduced to the oxidized form (dehydroascorbate), accompanied by a higher ascorbate peroxidase activity, was observed in Harvest 2 with respect to Harvest 1. Moreover, a decrease of the ascorbate-generating enzymatic system, the γ-galactono-lactone dehydrogenase, was found at Harvest 2. The activity values of the NADP-dependent dehydrogenases analyzed seem to indicate that a lower NADPH synthesis may occur in fruits which underwent lower temperature conditions. In spite of the important changes observed in the oxidative metabolism in fruits subjected to lower temperature, no oxidative stress appears to occur, as indicated by the lipid peroxidation and protein oxidation profiles. Thus, the antioxidative systems of pepper fruits seem to be involved in the response against temperature changes.     

Dual Enzyme Mimics Based on Metal–Ligand Cross-Linking Strategy for Accelerating Ascorbate Oxidation and Enhancing Tumor Therapy

The development of high-efficiency nanozymes is of great significance in the field of nanozymology, because this is one of the prerequisites for the sophisticated performance of nanozymes. Herein, the developed metal–ligand cross-linking strategy engineers porous carbon nanorod supported ultra-small iron carbide nanoparticles that possess excellent oxidase-like and peroxidase-like enzyme activities. The fabricated nanozyme can efficiently accelerate the oxidation of ascorbate (AA) to enhance cancer cells ablation efficacy. Due to the nanozyme having great surface atoms utilization ratio and large specific surface area, the AA can be rapidly and completely autoxidized within 20 min. Mechanism research demonstrates that the nanozyme's first activation of O₂ to generate superoxide free radicals (O₂^•−) via the oxidase-like pathway, then the O₂^•− directly oxidizes AA and produces hydrogen peroxide (H₂O₂). Simultaneously, the H₂O₂ transforms into the toxic hydroxyl radical through the peroxidase-like pathway and induces tumor cell death. Further in vitro and in vivo assays show the significant enhancement of the anti-tumor efficacy through AA oxidation which is catalyzed by the developed nanozyme. It is expected that this work will benefit not only the development of other efficient nanozymes, but also future advances in the field of AA oxidation induced tumor therapy.     

Metal-Catalyzed Oxidation of Ascorbate, Deoxyribose and Linoleic Acid as Affected by Phytic Acid in a Model System

Antioxidant activity of phytate was investigated in metal-catalyzed model systems. In a dose-dependent manner, phytate facilitated oxidation of Fe (II) to Fe (III) and inhibited formation of thiobarbituric acid-reactive substances (TBARS) from Fe (II)- or hemeprotein-catalyzed deoxyribose degradation. In the presence of 100 μM Fe (III), phytate inhibited reduction of Fe (III) to Fe (II) by 100 μM ascorbic acid and it consequently inhibited ascorbate oxidation. Phytate inhibited hemeprotein- and H₂O₂-catalyzed TBARS formation from linoleic acid micelles. Inhibition by phytate of iron + ascorbate-dependent lipid peroxidation depended on the concentration of ascorbate. These results indicate that phytate may be a useful antioxidant in the protection against oxidative deterioration of foods.