Effects Of Oxidative Modification Research Articles

Effect of Oxidative Modification by Peroxyl Radical on the Characterization and Identification of Oxidative Aggregates and In Vitro Digestion Products of Walnut (Juglans regia L.) Protein Isolates.

Walnut protein is a key plant protein resource due to its high nutritional value, but walnuts are prone to oxidation during storage and processing. This article explored the oxidative modification and digestion mechanism of walnut protein isolates by peroxyl radical and obtained new findings. SDS-PAGE and spectral analysis were used to identify structural changes in the protein after oxidative modification, and LC-MS/MS was used to identify the digestion products. The findings demonstrated that as the AAPH concentration increased, protein carbonyl content increased from 2.36 to 5.12 nmol/mg, while free sulfhydryl content, free amino content, and surface hydrophobicity decreased from 4.30 nmol/mg, 1.47 μmol/mg, and 167.92 to 1.72 nmol/mg, 1.13 μmol/mg, and 40.93 nmol/mg, respectively. Furthermore, the result of Tricine-SDS-PAGE in vitro digestion revealed that protein oxidation could cause gastric digestion resistance and a tendency for intestinal digestion promotion. Carbonyl content increased dramatically during the early stages of gastric digestion and again after 90 min of intestine digestion, and LC-MS/MS identified the last digestive products of the stomach and intestine as essential seed storage proteins. Oxidation causes walnut proteins to form aggregates, which are then re-oxidized during digestion, and proper oxidative modification may benefit intestinal digestion.

Effect of oxidative modification on physicochemical and functional properties of soybean polysaccharides

Oxidized soybean polysaccharides (OSSPS-1 and OSSPS-2) were prepared. Their structure was characterized, and their physicochemical and functional properties were evaluated. Structural analysis showed that the hydroxyl groups of soybean polysaccharides (SSPS) were oxidized to carboxyl groups. The molecular weight decreased from 1.5 × 105 Da (SSPS) to 7.2 × 104 Da (OSSPS-1) and 7.0 × 104 Da (OSSPS-2), respectively. The carboxyl content of SSPS, OSSPS-1 and OSSPS-2 was 1.79%, 6.08% and 9.45%, respectively. Uronic acid content of SSPS, OSSPS-1 and OSSPS-2 was 4.15%, 7.39% and 10.29%, respectively. Compared with SSPS, OSSPS-1 and OSSPS-2 showed decreased emulsifying property. Oxidative modification greatly reduced the viscosity of SSPS and changed their viscoelasticity. Whereas, oxidative modification improved a series of viscosity-related functional properties of SSPS, such as fat binding capacity, bile acid binding capacity, hypoglycemic effect. The antioxidant and antibacterial activities of SSPS were enhanced after oxidative modification. OSSPS-1 possessed higher DPPH scavenging ability, ferrous iron chelating ability and reducing power than OSSPS-2, but OSSPS-2 showed better antibacterial activities than OSSPS-1. The result revealed that oxidative modification had a significant effect on the structure of SSPS, which further affected the functional properties and biological activities of SSPS.

Effect of oxidative modification by reactive oxygen species (ROS) on the aggregation of whey protein concentrate (WPC)

The effects of reactive oxygen species (ROS) on the oxidative aggregation of whey protein concentrate (WPC) were studied. Increasing the oxidation time resulted in the accumulation of carbonyl groups, a decrease in α-helix structures, an increase in disordered structures and the aggregation of secondary structures. The surface hydrophobicity decreased and the zeta potential increased at the beginning of oxidation, indicating that electrostatic interactions were the cause of the noncovalent aggregation of the whey protein. Covalent aggregates were examined in terms of the sulfhydryl/disulfide content (total SH/SS), molecular weight and carbonyls, with the results implying that covalent interactions included protein-protein cross-linking, carbonyl cross-linking, and aromatic side chain cross-linking but excluded the cross-linking of sulfur-containing amino acid residues. The solubility and stability of initial aggregations were high due to flexible structures, while upon further oxidation, the solubility and stability worsened, consist with the soluble protein content and stability index.

Effects of oxidative modification by malondialdehyde on the in vitro digestion properties of rice bran protein

As a secondary oxidation product derived during rice bran oxidative rancidity, malondialdehyde (MDA) was selected to study the impact of oxidative rancidity on the digestion properties of rice bran protein. MDA modification promoted the content of protein carbonyl groups and disulfide bonds from 2.0 to 10.34 nmol/mg, 12.04–16.51 nmol/mg, respectively. The results of FT-IR, intrinsic fluorescence spectra, surface hydrophobicity, molecular weight distribution and protein electrophoresis implied that MDA changed the secondary structure of rice bran protein, and promoted protein aggregation and cross-link through non-disulfide covalent bonds. Besides, increasing concentration of MDA caused the loss of degradation potential of protein, which accompanied by the loss of pepsin and trypsin digestibility from 33.86 to 24.29%, 70.10 to 47.05%, respectively. Furthermore, MDA treatment led to the decrease in antioxidant activities of digestion products, which might be attributed to the less formation of digestion products with molecular weight of 500–1500 Da. Correlation analysis between parameters of rice bran protein oxidation and protein digestion revealed that rice bran protein oxidation was significantly related to the reduction of digestion parameters. Overall, incubation with MDA altered the structure of rice bran protein, which had a significant correlation with the deterioration of digestion properties.

Effects of hydroxyl radical oxidation on myofibrillar protein and its susceptibility to μ-calpain proteolysis

In the present study, the modification of myofibrillar protein (MP) by hydroxyl radicals (·OH) and the effects of oxidative modification on the proteolysis of MP by μ-calpain were investigated. Isolated MP was exposed to different oxidation conditions and then incubated with μ-calpain. With increasing H2O2 concentration, the carbonyl and dityrosine contents as well as the surface hydrophobicity of the MP increased, while the total sulfhydryl groups and tryptophan fluorescence intensity gradually decreased. Disulfide bonds and other covalent bonds resulted in the cross-linking and aggregation of proteins. Increasing oxidant concentration resulted in the α-helix content decreasing from 19.19% to 17.32% whereas the β-sheet content increased from 21.59% to 26.47%. Protein oxidation increased the proteolytic susceptibility of actin, but inhibited the proteolysis of myosin heavy chain, troponin T, and desmin. Overall, our data demonstrate that ·OH can change the structure of MP and its susceptibility to proteolysis by μ-calpain, providing mechanistic information that links protein oxidation with proteolysis.

Effects of oxidative modification on the functional, conformational and gelling properties of myofibrillar proteins from Culter alburnus

Protein oxidation is a critical process in the deterioration and spoilage of fish and related commodities during processing and storage. In this study, the hydroxyl radical generation system (HRGS) was used to simulate the effect of oxidation on the functional, conformational and gelling properties of topmouth culter (Culter alburnus) myofibrillar proteins (MP). Additionally, the effects of oxidation on the gel-forming abilities of MP were also systematically analyzed from the perspective of intermolecular interaction forces. Oxidation was shown to decrease the total sulfhydryl content, increase the surface hydrophobicity, and induce conformational changes in MP. Rheological analysis showed that oxidation reduced the gel strength. Water holding capacity (WHC) and low-field nuclear magnetic resonance (LF-NMR) analyses showed that low oxidation could enhance water binding of protein matrix, while high-degree oxidation could substantially reduce the gelling properties of MP. The selective solubility of MP gel proved that oxidation could reduce the content of ionic and hydrogen bonds and increase hydrophobic interactions. All the results indicate that oxidation could alter the intermolecular interactions between protein-protein and protein-water molecules, due to irregular unfolding and inhibition of the cross-linking of amino acid side chains, leading to reduction in the quality and function of fish and related products.

Effects of oxidative modification by 13-hydroperoxyoctadecadienoic acid on the structure and functional properties of rice protein

13-hydroperoxyoctadecadienoic acid (13-HPODE) was selected as lipid peroxidation primary products during rice ageing to investigate the effects of lipid hydroperoxide modification on the structural characteristics and functional properties of rice protein. Incubation of rice protein with 13-HPODE resulted in protein carbonylation and loss of protein sulfhydryl groups in a concentration-dependent manner. FT-IR evaluated the effects of 13-HPODE on rice protein, and the results indicated increasing concentration of 13-HPODE resulted in continuous loss of α-helix, β-turn and random coil structure, and increase in β-sheet content and amino acid side chains. The content of soluble protein aggregates gradually increased, accompanied by protein crosslink via disulfide bonds. 13-HPODE had a negative impact on the solubility, water holding capacity, foaming capacity, and foam stability of rice protein. 13-HPODE could promote oil holding capacity of rice protein. With the concentration of 13-HPODE below 0.1 mmol/L, emulsifying activity index (EAI) and emulsifying stability index (ESI) of rice protein gradually increased, which due to gradual increase in rice protein surface hydrophobicity and flexibility. However, at relatively high concentration of 13-HPODE (above 1 mmol/L), the adverse effect in EAI and ESI was observed, which might be attributed to a decrease in surface hydrophobicity and protein aggregates formation.

Effects of oxidative modification on textural properties and gel structure of pork myofibrillar proteins

Isolated myofibrillar protein (MP) was treated by the oxidation system of FeCl3 (0.01 mM) at four different H2O2 concentrations (0, 1, 10, 20 mM). The oxidation degree was determined by measuring the carbonyl and total sulphydryl values. The structure and physicochemical properties of MP gels were investigated by water holding capacity (WHC) evaluation, sodium dodecyl sulfate-polyacryl amide gel electrophoresis (SDS-PAGE), texture profile analysis (TPA), Raman spectroscopy, and NMR transverse relaxation (T2). The results of carbonyls and total sulphydryls indicated that oxidation degree of MP increased with increasing H2O2 concentration. TPA showed that moderate oxidation (10 mM H2O2) could improve the hardness, springiness, gumminess and cohesiveness of MP gels, but not contribute to the maintenance of their WHC, probably due to severe depolymerization of MPs, unfolding of α-helix, exposure of the hydrophobic groups and the migration of protein-associated water (T2b) and intra-myofibrillar water (T21) to the longer relaxation time.

Effects of oxidative modification on thermal aggregation and gel properties of soy protein by peroxyl radicals

SummaryEffects of protein oxidation on thermal aggregation and gel properties of soy protein by 2,2′‐azobis (2‐amidinopropane) dihydrochloride (AAPH)‐derived peroxyl radicals were investigated in this article. Incubation of soy protein to increase concentration of AAPH resulted in a decrease in particle size and content of thermal aggregates during thermal‐induced denaturation. Protein oxidation resulted in a decrease in water‐holding capacity (WHC), gel hardness and gel strength of soy protein gel. An increase in coarseness and interstice of the gel network was accompanied by uneven distribution of interstice as extent of oxidation of soy protein increased. A decrease in disulphide content and formation of oxidation aggregates in the process of oxidative modification were contributed to the decline of particle size and content of thermal aggregates during thermal‐induced denaturation, leading to a decrease in WHC, gel hardness and gel strength of soy protein gel.

Abstract 222: Oxidative Modification of Extracellular Matrix Proteins Alters the Hsp90 Interactome in Human Umbilical Vein Endothelial Cells

Lipid peroxidation increases the production of thiol-reactive α, β-unsaturated aldehydes such as 4-hydroxy-2-nonenal (4-HNE). Exposure of endothelial cells (EC) to 4-HNE impairs cell function. Interestingly, heat shock protein 90 (hsp90), which interacts with a multitude of client proteins, is upregulated under conditions that promotes oxidative stress. However, to our knowledge no one has examined the effects of oxidative modification of matrix proteins on cell function. Here we hypothesize that oxidative modification of matrix perturbs EC function with respect to the hsp90 interactome. To test this hypothesis, we treated gelatin-coated culture dishes with 10 μM Linoleic Acid (LA) under conditions that promoted oxidation. Dishes were washed free of excess LA and seeded with human umbilical vein EC. Native dishes without LA treatment were used as control. The hsp90 client proteins were identified by immunoprecipitation of hsp90 and nanoLC-MS/MS analysis. Oxidative modification of gelatin caused a marked shift in the hsp90-interactome (n = 4). EC maintained on LA-treated gelatin expressed more hsp90 (1.5 X) than controls. Only ~33% of the proteins were present in both groups at similar levels. Hsp90 client proteins in EC maintained on LA-treated gelatin also had increased levels of DNA repair protein BRCA2, protein kinase Tec, protein phosphatase RPTP-rho, ubiquitin ligase Pellino 3, chaperone protein nucleophosmin, retinoic acid receptor, 2 histone deacetylases (e.g. Sin3b), 4 transcription factors (e.g. Prox1), 5 cytoskeleton protein and stress fibers (e.g. tubulin), 9 ribosomal proteins. GO analysis revealed that most of these proteins are involved in stress responses such as protein synthesis, degradation, stress fiber formation, transcription repression, DNA repair and senescence. These data show that EC enter into a stress-response status with marked alterations in the hsp90 interactome upon sensing oxidative modification of extracellular matrix proteins. Such changes may play a role in impaired anti-atherogenic responses in the vessel wall.

The effects of oxidative modification on the interaction of low density lipoprotein with collagen

The effects of oxidative modification on the interaction of low density lipoprotein with collagen

Prothrombotic Consequences of the Oxidation of Fibrinogen and their Inhibition by Aspirin.

Oxidant stress leads to covalent oxidative modification of several plasma proteins, chief among which is fibrinogen. Aspirin can nonenzymatically acetylate fibrinogen's lysine residues, the functional groups most susceptible to oxidative modification. Because oxidation of fibrinogen may occur in the atheromatous environment, we studied the effects of oxidative modification on fibrinogen function and the consequences of acetylation by aspirin on fibrinogen's susceptibility to oxidation and functional properties. We exposed fibrinogen to Fe(3+) ascorbate for 1 hour and showed that the carbonyl/protein molar ratio increased from 0.71 +/- 0.18 to 2.86 +/- 0.50 mol carbonyl/mol protein (P < 0.02) with an accompanying reduction in the alpha-helical content of the protein from 34% to 29%. Exposure of fibrinogen to aspirin led to acetylation of lysine residues and inhibition of oxidation. Oxidized fibrinogen was more readily able to form fibrin, and acetylation prevented this enhancement of clot formation. Oxidized fibrinogen also supported platelet aggregation better than did native, unoxidized fibri ogen, and aretylation of fibrinogen prior to oxidation prevented the enhanced platelet aggregation. Oxidized fibrinogen was less effective in stimulating plasminogen activation by tissue-type plasminogen activator (tPA), with a catalytic efficiency that was reduced by 88% compared with native, unoxislized fibrinogen; metylated fibrinogen, by contrast, enhanced plasminogen activation by t-PA with a catalytic efficiency that was increased by 18% compared with native, anoxidized fibrinogen (P < 0.05) and was increased by 51% compared with oxidized fibrinogen (P < 0.05). Acetylation prevented the reduction in catalytic efficiency induced by oxidation. These data show that oxidized fibrinogen manifests prothrombotic effects that can be prevented by acetylation and suggest that inhibition of fibrinogen oxidation may be an additional antithrombotic benefit of aspirin therapy.

3.P.141 Effect of oxidative modification of low density lipoprotein on its binding to mouse peritoneal macrophages mediated by endogenous and exogenous lipoprotein lipase

3.P.141 Effect of oxidative modification of low density lipoprotein on its binding to mouse peritoneal macrophages mediated by endogenous and exogenous lipoprotein lipase

Effects of oxidative modification of cholesterol in isolated low density lipoproteins on cultured smooth muscle cells

It has been proposed that low density lipoprotein (LDL) must undergo oxidative modification before it can participate in atherosclerosis. The present paper studied the effect of cholesterol oxidation in LDL on cultured vascular smooth muscle cells. LDL was oxidized by cholesterol oxidase (3-beta-hydroxy-steroid oxidase) which catalyzes the oxidation of cholesterol to 4-cholesten-3 one and other oxidized cholesterol derivatives. Cholesterol oxidase treatment of LDL did not result in lipid peroxidation. Cultured rabbit aortic smooth muscle cells were morphologically changed following exposure to cholesterol oxidized LDL. Nile red, a hydrophobic probe which can selectively stain intracellular lipid droplets, was applied to detect the cellular lipid content after treatment with oxidized or non-oxidized LDL cholesterol. LDL which did not undergo oxidation of its cholesterol had no effect on the cells. However, cellular nile red fluorescence intensity was increased as the pre-incubation time of cholesterol oxidase with LDL increased. This was supported by HPLC analysis which revealed that the oxidized cholesterol content of treated cells increased. These findings suggest that cholesterol oxidation of LDL can alter lipid deposition in the cells and change cell morphology. The oxidation of cholesterol in vivo may play an important role in the modification of LDL which could contribute to the generation of the lipid-laden foam cells.

Studies in the Reaction of Formaldehyde with Unmodified, Modified, and Dyed Celluloses: Part III: The Reaction of Formaldehyde with Oxycelluloses

The reaction of formaldehyde with oxycelluloses obtained by the oxidation of cotton cellulose with four oxidizing agents is investigated. The rate and the extent of the reaction with these oxycelluloses before and after their treatment with chlorous acid and sodium borohydride have been studied to see the effect of oxidative modification of cellulose on its reaction with formaldehyde. It is observed that the rate and extent of reaction depend upon the nature and extent of oxidation, the change in the fine structure of cellulose during oxidation, the subsequent treatments, and the carboxyl content. A tentative mechanism for the inhibiting action of carboxyl groups present in the anhydroglucose units of the cellulosic material has been suggested.