Formation Of Covalent Linkage Research Articles

Wheat gluten structure and (non–)covalent network formation during deep-fat frying

The aim of this work was to investigate wheat gluten protein network structure throughout the deep-frying process and evaluate its contribution to frying-induced micro- and macrostructure development. Gluten polymerization, gluten-water interactions, and molecular mobility were assessed as a function of the deep-frying time (0 – 180 s) for gluten-water model systems of differing hydration levels (40 – 60 % moisture content). Results showed that gluten protein extractability decreased considerably upon deep frying (5 s) mainly due to glutenin polymerization by disulfide covalent cross-linking. Stronger gliadin and glutenin protein–protein interactions were attributed to the formation of covalent linkages and evaporation of water interacting with protein chains. Longer deep-frying (> 60 s) resulted in progressively lower protein extractabilities, mainly due to the loss in gliadin protein extractability, which was associated with gliadin co-polymerization with glutenin by thiol-disulfide exchange reactions. The mobility of gluten polymers was substantially reduced during deep-frying (based on the lower T2 relaxation time of the proton fraction representing the non-exchanging protons of gluten) and gluten proteins gradually transitioned from the rubbery to the glassy state (based on the increased area of said protons). The sample volume during deep-frying was strongly correlated to the reduced protein extractability (r = –0.792, p < 0.001) and T2 relaxation time of non-exchanging protons of gluten proteins (r = –0.866, p < 0.001) thus demonstrating that the extent of gluten structural expansion as a result of deep-frying is dictated both by the polymerization of proteins and the reduction in their molecular mobility.

Radical Mediated Rapid In Vitro Formation of c-Type Cytochrome.

A cytochrome c552 mutant from Thermus thermophilus HB8 (rC552 C14A) was reported, where the polypeptide with replaced Cys14 by alanine, overexpressed in the cytosol of E. coli. The apo-form of the C14A mutant (apo-C14A) without the original prosthetic group was obtained by simple chemical treatments that retained compact conformation amenable to reconstitution with heme b and zinc(II)-protoporphyrin(IX), gradually followed by spontaneous formation of a covalent bond between the polypeptide and porphyrin ring in the reconstituted apo-C14A. Further analysis suggested that the residual Cys11 and vinyl group of the porphyrin ring linked through the thiol-ene reaction promoted by light under ambient conditions. In this study, we describe the kinetic improvement of the covalent bond formation in accordance with the mechanism of the photoinduced thiol-ene reaction, which involves a thiyl radical as a reaction intermediate. Adding a radical generator to the reconstituted C14A mutant with either heme-b or zinc(II) porphyrin accelerated the bond-forming reaction, which supported the involvement of a radical species in the reaction. Partial observation of the reconstituted C14A in a dimer form and detection of sulfuryl radical by EPR spectroscopy indicated a thiyl radical on Cys11, a unique cysteinyl residue in rC552 C14A. The covalent bond forming mediated by the radical generator was also adaptable to the reconstituted apo-C14A with manganese(II)-protoporphyrin(IX), which also exhibits light-mediated covalent linkage formation. Therefore, the radical generator extends the versatility of producing c-type-like cytochrome starting from a metallo-protoporphyrin(IX) and the apo-C14A instantaneously.

Hydrogel tapes for fault-tolerant strong wet adhesion

Fast and strong bio-adhesives are in high demand for many biomedical applications, including closing wounds in surgeries, fixing implantable devices, and haemostasis. However, most strong bio-adhesives rely on the instant formation of irreversible covalent crosslinks to provide strong surface binding. Repositioning misplaced adhesives during surgical operations may cause severe secondary damage to tissues. Here, we report hydrogel tapes that can form strong physical interactions with tissues in seconds and gradually form covalent bonds in hours. This timescale-dependent adhesion mechanism allows instant and robust wet adhesion to be combined with fault-tolerant convenient surgical operations. Specifically, inspired by the catechol chemistry discovered in mussel foot proteins, we develop an electrical oxidation approach to controllably oxidize catechol to catecholquinone, which reacts slowly with amino groups on the tissue surface. We demonstrate that the tapes show fast and reversible adhesion at the initial stage and ultrastrong adhesion after the formation of covalent linkages over hours for various tissues and electronic devices. Given that the hydrogel tapes are biocompatible, easy to use, and robust for bio-adhesion, we anticipate that they may find broad biomedical and clinical applications.

Modeling the Binding and Conformational Energetics of a Targeted Covalent Inhibitor to Bruton's Tyrosine Kinase.

Targeted covalent inhibitors (TCIs) bind to their targets in both covalent and noncovalent modes, providing exceptionally high affinity and selectivity. These inhibitors have been effectively employed as inhibitors of protein kinases, with Taunton and coworkers (Nat. Chem. Biol. 2015, 11, 525-531) reporting a notable example of a TCI with a cyanoacrylamide warhead that forms a covalent thioether linkage to an active-site cysteine (Cys481) of Bruton's tyrosine kinase (BTK). The specific mechanism of the binding and the relative importance of the covalent and noncovalent interactions is difficult to determine experimentally, and established simulation methods for calculating the absolute binding affinity of an inhibitor cannot describe the covalent bond-forming steps. Here, an integrated approach using alchemical free-energy perturbation and QM/MM molecular dynamics methods was employed to model the complete Gibbs energy profile for the covalent inhibition of BTK by a cyanoacrylamide TCI. These calculations provide a rigorous and complete absolute Gibbs energy profile of the covalent modification binding process. Following a classic thiol-Michael addition mechanism, the target cysteine is deprotonated to form a nucleophilic thiolate, which then undergoes a facile conjugate addition to the electrophilic functional group to form a bond with the noncovalently bound ligand. This model predicts that the formation of the covalent linkage is highly exergonic relative to the noncovalent binding alone. Nevertheless, noncovalent interactions between the ligand and individual amino acid residues in the binding pocket of the enzyme are also essential for ligand binding, particularly van der Waals dispersion forces, which have a larger contribution to the binding energy than the covalent component in absolute terms. This model also shows that the mechanism of covalent modification of a protein occurs through a complex series of steps and that entropy, conformational flexibility, noncovalent interactions, and the formation of covalent linkage are all significant factors in the ultimate binding affinity of a covalent drug to its target.

Tuning the Surface Chemistry of Second-Harmonic-Active Lithium Niobate Nanoprobes Using a Silanol-Alcohol Condensation Reaction.

The surface functionalization of nanoparticles (NPs) is of great interest for improving the use of NPs in, for example, therapeutic and diagnostic applications. The conjugation of specific molecules with NPs through the formation of covalent linkages is often sought to provide a high degree of colloidal stability and biocompatibility, as well as to provide functional groups for further surface modification. NPs of lithium niobate (LiNbO3) have been explored for use in second-harmonic-generation (SHG)-based bioimaging, expanding the applications of SHG-based microscopy techniques. The efficient use of SHG-active LiNbO3 NPs as probes will, however, require the functionalization of their surfaces with molecular reagents such as polyethylene glycol and fluorescent molecules to enhance their colloidal and chemical stability and to enable a correlative imaging platform. Herein, we demonstrate the surface functionalization of LiNbO3 NPs through the covalent attachment of alcohol-based reagents through a silanol-alcohol condensation reaction. Alcohol-based reagents are widely available and can have a range of terminal functional groups such as carboxylic acids, amines, and aldehydes. Attaching these molecules to NPs through the silanol-alcohol condensation reaction could diversify the reagents available to modify NPs, but this reaction pathway must first be established as a viable route to modifying NPs. This study focuses on the attachment of a linear alcohol functionalized with carboxylic acid and its use as a reactive group to further tune the surface chemistry of LiNbO3 NPs. These carboxylic acid groups were reacted to covalently attach other molecules to the NPs using copper-free click chemistry. This derivatization of the NPs provided a means to covalently attach polyethylene glycols and fluorescent probes to the NPs, reducing NP aggregation and enabling multimodal tracking of SHG nanoprobes, respectively. This extension of the silanol-alcohol condensation reaction to functionalize the surfaces of LiNbO3 NPs can be extended to other types of nanoprobes for use in bioimaging, biosensing, and photodynamic therapies.

Designing Adaptive Binders for Microenvironment Settings of Silicon Anode Particles.

This study reports the concept of an "adaptive binder" to address the silicon anode challenge in Li-ion batteries. Binders exhibit adaptable capabilities upon gradual changes in the microenvironments surrounding silicon particles during anodic expansion-shrinkage cycles. Long, flexible binder chains are repositioned and reoriented upon the gradual formation of Si-micro-environments (Si-μ-env) during the early battery cycles. At this stage, the chemical interactions between the polymeric binders are reversible hydrogen bonds. As the Si-μ-env become stably set by repeated battery cycles, the chemical interactions exhibit reversible-to-irreversible transitions by the formation of covalent linkages between the binder polymers at the later stage of cycles. The binder polymer showing the aforementioned adaptive properties is hyaluronic acid, which has never been explored as a silicon-anode binder material, onto which the plant-inspired adhesive phenolic moiety, gallol (1,2,3-trihydroxybenzene), is conjugated (HA-GA) for stable adhesion to the surfaces of silicon particles. It is confirmed that the HA-GA binder can maintain a charge capacity that is approximately 3.3 times higher (1153 mAh g-1 ) than that of the nonconjugated HA binder (347 mAh g-1 ) after 600 cycles even at a rapid charge/discharge rate of 1 C (3500mA g-1 ), indicating that adaptive properties are an important factor to consider in designing silicon-anode binders.

Proton Conductive Membranes from Covalently Cross‐Linked Poly(Acrylate)/Silica Interpenetrating Networks

AbstractThe preparation of hybrid proton conductive membranes that comprise of covalently linked interpenetrating polymer and inorganic networks is reported. The hybrid membranes are synthesized via simultaneous photo‐initiated polymerization and sol–gel processing. The simultaneous processing permeates fabrication of the membranes that comprises covalently cross‐linked polymeric and inorganic networks. The membranes are characterized by attenuated total reflectance‐Fourier transform infrared spectroscopy, scaning electron microsopy, thermogravimetric analysis, differential scanning calorimetry, in order to confirm their chemical composition, structure, and morphology. An addition of 3‐methacryloxypropyl trimethoxysilane into the sol–gel composition allows the formation of covalent linkages between polymeric and inorganic networks, which facilitates a uniform distribution of the molecular components across the fabricated membranes. The incorporation of the silica network leads to an increase in water retention and proton conductivity of hybrid membranes as compared to their purely polymeric analogues.

Effect of surfactant-induced competitive displacement of whey protein conjugated to acid- or alkali-extracted potato pectin on emulsion stability

Covalently linked protein–polysaccharide conjugate pre-adsorbed to the interface often shows more enhanced resistance to displacement induced by competitively adsorbing small molecule surfactant than the pure protein component. The objective of this study was to investigate the effect of surfactant-induced competitive displacement of whey protein–potato pectin conjugate pre-adsorbed to oil droplet surfaces on the stability of the oil-in-water emulsion. Potato pectin extracted in either an acidic or alkaline condition was conjugated to bovine milk whey protein using the Maillard reaction. The formation of covalent linkage between the protein and pectin moieties was confirmed using sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Atomic force microscopy studies of the interfacial films of the Maillard conjugates formed on flat water surfaces revealed that the alkali-extracted potato pectin provided more enhanced resistance to surfactant-induced competitive displacement from the air–water interface than the acid-extracted potato pectin. These results indicate that galactan side chains having an ability to self-assemble and form network structures had been preserved to a larger degree during the alkali-extraction. Furthermore, the alkali-extracted potato pectin prevented coalescence-induced increases in the oil droplet diameter in the oil-in-water emulsions prepared using the Maillard conjugate as the emulsifier upon the addition of up to 38.7 mM of the Tween 20 surfactant while maintaining relatively high levels of the surface load of protein (>0.8 mg/m2). The present results demonstrate that the molecular structure of the polysaccharide moiety of protein–polysaccharide conjugate has significant impacts on its resistance to competitive displacement and emulsion stability.

Novel Bovine Serum Albumin Protein Backbone Reassembly Study: Strongly Twisted β-Sheet Structure Promotion upon Interaction with GO-PAMAM.

This study investigates the formation of a graphene oxide-polyamidoamine dendrimer complex (GO-PAMAM) and its association and interaction with bovine serum albumin (BSA). Fourier-transform infrared spectrometry and X-ray photoelectron spectrometry indicated the formation of covalent linkage between the GO surface and PAMAM with 7.22% nitrogen content in the GO-PAMAM sample, and various interactions between BSA and GO-PAMAM, including π-π* interactions at 291.5 eV for the binding energy value. Thermogravimetric analysis highlighted the increasing thermal stability throughout the modification process, from 151 to 192 °C for the 10% weight loss temperature. Raman spectrometry and X-ray diffraction analysis were used in order to examine the complexes’ assembly, showing a prominent (0 0 2) lattice in GO-PAMAM. Dynamic light scattering tests proved the formation of stable graphenic and graphenic-protein aggregates. The secondary structure rearrangement of BSA after interaction with GO-PAMAM was investigated using circular dichroism spectroscopy. We have observed a shift from 10.9% β-sheet composition in native BSA to 64.9% β-sheet composition after the interaction with GO-PAMAM. This interaction promoted the rearrangement of the protein backbone, leading to strongly twisted β-sheet secondary structure architecture.

Flavonoids with Vicinal Hydroxyl Groups Inhibit Human Calcitonin Amyloid Formation.

Human calcitonin (hCT) is a 32-residue peptide hormone that can aggregate into amyloid fibrils and cause cellular toxicity. In this study, we investigated the inhibition effects of a group of polyphenolic molecules on hCT amyloid formation. Our results suggest that the gallate moiety in epigallocatechin-3-gallate (EGCG), a well-recognized amyloid inhibitor, is not critical for its inhibition function in the hCT amyloid formation. Our results demonstrate that flavonoid compounds, such as myricetin, quercetin, and baicalein, that contain vicinal hydroxyl groups on the phenyl ring effectively prevent hCT fibrillization. This structural feature may also be applied to non-flavonoid polyphenolic inhibitors. Moreover, our results indicate a plausible mechanistic role of these vicinal hydroxyl groups which might include the oxidation to form a quinone and the subsequent covalent linkage with amino acid residues such as lysine or histidine in hCT. This may further disrupt the crucial electrostatic and aromatic interactions involved in the process of hCT amyloid fibril formation. The inhibition activity of the polyphenolic compounds against hCT fibril formation may likely be attributed to a combination of factors such as covalent linkage formation, aromatic stacking, and hydrogen bonding interactions.

A suicide enzyme catalyzes multiple reactions for biotin biosynthesis in cyanobacteria.

In biotin biosynthesis, the conversion of pimeloyl intermediates to biotin is catalyzed by a universal set of four enzymes: BioF, BioA, BioD and BioB. We found that the gene homologous to bioA, the product of which is involved in the conversion of 8-amino-7-oxononanoate (AON) to 7,8-diaminononanoate (DAN), is missing in the genome of the cyanobacterium Synechocystis sp. PCC 6803. We provide structural and biochemical evidence showing that a novel dehydrogenase, BioU, is involved in biotin biosynthesis and functionally replaces BioA. This enzyme catalyzes three reactions: formation of covalent linkage with AON to yield a BioU-DAN conjugate at the ε-amino group of Lys124 of BioU using NAD(P)H, carboxylation of the conjugate to form BioU-DAN-carbamic acid, and release of DAN-carbamic acid using NAD(P)+. In this biosynthetic pathway, BioU is a suicide enzyme that loses the Lys124 amino group after a single round of reaction.

Identification of cysteine thiol‐based linkages in ADAMTS13 in support of a non‐proteolytic regulation of von Willebrand factor

BackgroundADAMTS13, a plasma metalloprotease, cleaves von Willebrand factor (VWF) to regulate its function. Additionally, ADAMTS13 is thought to regulate lateral association of VWF multimers to form fibrillar structures through its free thiols. ObjectiveThe purpose of the present study is to obtain direct evidence for ADAMTS13 to engage in thiol/disulfide exchange reactions. MethodsCovalent complexes between ADAMTS13 and VWF were determined by agarose gel electrophoresis under nonreducing conditions. Free thiols in ADAMST13 were identified by a reversed phase high‐performance liquid chromatography electrospray ionization quadrupole time‐of‐flight mass spectrometry system. ResultsWe demonstrate formation of covalent linkage between ADAMTS13 and VWF, which is time, concentration, temperature, and shear dependent. This interaction is independent of proteolytic activity of ADAMTS13 but depends on the C‐terminal domains comprising the fifth through eighth thrombospondin type 1 repeats and C1r/C1s, Uegf, Bmp1 (CUB) domains. The interaction can be blocked by thiol‐reactive agents, indicating that association is accomplished through disulfide bridge formation. Several partially reduced free thiols are identified in ADAMTS13, with cysteines 1254 and 1275 being the most prominent, although a point mutation (C1275S) in ADAMTS13 does not alter its ability to form covalent linkages with VWF. This suggests functionally relevant disulfide plasticity in ADAMTS13. Interestingly, ADAMTS13 also forms homo‐oligomers under the same conditions as required for the generation of hetero‐oligomeric complexes of ADAMTS13 and VWF. ConclusionsOur results suggest that a dynamic network of free thiols in ADAMTS13 undergoing intra‐ and inter‐molecular redox reactions may add another layer of regulation to VWF function under various conditions.

Photosensitizer Tailored Surface Functionalized Carbon Dots for Visible Light Induced Targeted Cancer Therapy.

Herein, a photosensitizer (riboflavin) tailored surface functionalized carbon dot (RCD1s) was designed to utilize it in visible light induced targeted cancer therapy. At first, phenylboronic acid appended biotinylated blue emitting carbon dot (CD1s) was synthesized. Riboflavin having "diol" moiety was covalently linked with this CD1s to prepare RCD1s by using complementary boronate-diol linkage. Lewis acid-base interaction facilitated the covalent linkage formation between the surface functionalizing agent of CD1s and riboflavin to develop water-soluble, green emitting RCD1s. Interestingly, this newly synthesized RCD1s has the ability to produce reactive oxygen species (ROS) such as hydroxyl and superoxide radicals under exposure of visible light (wavelength: 460-490 nm). These ROS also can destroy the structure of DNA by oxidative pathway. Thus, under irradiation of visible light (wavelength: 460-490 nm), RCD1s was found to kill HeLa and B16F10 melanoma cells over noncancer cell NIH3T3 by ∼5-fold higher efficacy through ROS induced oxidative DNA damage. The presence of biotin on the surface of the riboflavin tethered carbon dot is essential for the selective killing of cancer cells over normal cells. In the presence of UV light (340-420 nm), RCD1s showed no notable killing of cancer cells as well as normal cells. Besides, RCD1s in the presence of visible light selectively stained HeLa and B16F10 cells over noncancerous cell NIH3T3 by exploiting its fluorescence and cancer cell targeting moiety, biotin. Hence, the newly developed RCD1s can be utilized in theranostic applications including bioimaging and selective killing of cancer cells in the presence of visible light (460-490 nm).

Genetically Encoded Residue-Selective Photo-Crosslinker to Capture Protein-Protein Interactions in Living Cells

Summary The genetically encoded non-selective photo-crosslinkers suffer from unpredictable crosslinking sites and false positive interacting proteins, thus, the identification of protein interactions and mapping accurate interaction interfaces remain largely elusive in living systems. Here, we report genetically encoded, residue-selective protein photo-crosslinker enabling covalent crosslinking of the interacting proteins with proximal lysine, upon UV light activation in vitro and in living cells. Using this photo-crosslinker, we demonstrate a crosslinking strategy to capture protein-protein interactions with residue selectivity in a temporal-resolved manner. In addition, this crosslinking strategy produces the lysine-selective crosslinking site and predictable crosslinked peptide, which serve as the direct evidence for protein-protein interactions and facilitate mass spectrometry analysis. More importantly, this photo-crosslinker enables the capture of elusive enzyme-substrate interaction with directly interacting lysine and validation of acetylation site of the substrate. This strategy represents higher spatiotemporal resolution, accuracy, and reliability for investigating dynamic, transient, and weak protein-protein interactions in living systems.

Improved rheology and high‐temperature stability of hydrolyzed polyacrylamide using graphene oxide nanosheet

ABSTRACTHydrolyzed polyacrylamide (HPAM) is a polymer that extensively used in chemical industry and hydrocarbon extraction and refinery processes, but suffers a common problem of high‐temperature instability. This study improved high‐temperature rheological characteristics of HPAM by using novel graphene oxide (GO) nanosheets. Stable GO dispersions in aqueous HPAM were formulated, and their dynamic and viscoelastic behaviors were studied. The results showed that the addition of GO significantly increased the viscosities and high‐temperature stability of the base polymer fluid, as well as the elastic properties of the dispersion. Spectral data indicated the formation of covalent linkages and electrostatic hydrogen bonding between the GO and the HPAM functional groups, leading to enhanced stability and viscosity that is beneficial for high‐temperature oil recovery. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47582.

Triazole End-Grafting on Cellulose Nanocrystals for Water-Redispersion Improvement and Reactive Enhancement to Nanocomposites

Different from the conventional surface modification strategy, the end reaction based on the active aldehyde groups of cellulose nanocrystal (CNC) provides a targeted modification under the protection of its surface chemistry. With the purpose of promoting its redispersibility in water, the strategy of triazole end-grafting performed on CNC was proposed in this study, exhibiting the significant improvement on the redispersion and stability of nanocrystals in the aqueous suspension attributed to synergistic effect of steric stabilization and electrostatic repulsion. The end-modified CNC was then introduced into a natural rubber (NR) matrix to fabricate the composites with reactive compatibility from a thiol–ene click reaction. Ascribed to the formation of covalent linkage between nanofillers and matrix together with the architecture of the rigid percolating network, the mechanical properties of obtained composites were remarkably advanced. With the introduction of 10 wt % end-modified CNC, the tensile stre...

Carboxyl-rich plasma polymer surfaces in surface plasmon resonance immunosensing

Stable carboxyl-rich plasma polymers (PPs) were deposited onto the gold surface of surface plasmon resonance (SPR) chips under conditions that were chosen based on lumped kinetic model results. Carboxyl-rich films are of high interest for bio-applications thanks to their high reactivity, allowing the formation of covalent linkages between biomolecules and a surface. Accordingly, the monoclonal antibody, specific to human serum albumin (HSA), was immobilized and the performance of SPR immunosensors was evaluated by the immunoassay flow test. The developed sensors performed high level of stability and provided selective and high response to the HSA antigen solutions. The achieved results confirmed that the presented methodologies for the grafting of biomolecules on the gold surfaces have great potential for biosensing applications.

Identification of Substitutions and Small Insertion-Deletions Induced by Carbon-Ion Beam Irradiation in Arabidopsis thaliana.

Heavy-ion beam irradiation is one of the principal methods used to create mutants in plants. Research on mutagenic effects and molecular mechanisms of radiation is an important subject that is multi-disciplinary. Here, we re-sequenced 11 mutagenesis progeny (M3) Arabidopsis thaliana lines derived from carbon-ion beam (CIB) irradiation, and subsequently focused on substitutions and small insertion-deletion (INDELs). We found that CIB induced more substitutions (320) than INDELs (124). Meanwhile, the single base INDELs were more prevalent than those in large size (≥2 bp). In details, the detected substitutions showed an obvious bias of C > T transitions, by activating the formation of covalent linkages between neighboring pyrimidine residues in the DNA sequence. An A and T bias was observed among the single base INDELs, in which most of these were induced by replication slippage at either the homopolymer or polynucleotide repeat regions. The mutation rate of 200-Gy CIB irradiation was estimated as 3.37 × 10−7 per site. Different from previous researches which mainly focused on the phenotype, chromosome aberration, genetic polymorphism, or sequencing analysis of specific genes only, our study revealed genome-wide molecular profile and rate of mutations induced by CIB irradiation. We hope our data could provide valuable clues for explaining the potential mechanism of plant mutation breeding by CIB irradiation.

The plant cell-wall enzyme AtXTH3 catalyses covalent cross-linking between cellulose and cello-oligosaccharide

Cellulose is an economically important material, but routes of its industrial processing have not been fully explored. The plant cell wall – the major source of cellulose – harbours enzymes of the xyloglucan endotransglucosylase/hydrolase (XTH) family. This class of enzymes is unique in that it is capable of elongating polysaccharide chains without the requirement for activated nucleotide sugars (e.g., UDP-glucose) and in seamlessly splitting and reconnecting chains of xyloglucan, a naturally occurring soluble analogue of cellulose. Here, we show that a recombinant version of AtXTH3, a thus far uncharacterized member of the Arabidopsis XTH family, catalysed the transglycosylation between cellulose and cello-oligosaccharide, between cellulose and xyloglucan-oligosaccharide, and between xyloglucan and xyloglucan-oligosaccharide, with the highest reaction rate observed for the latter reaction. In addition, this enzyme formed cellulose-like insoluble material from a soluble cello-oligosaccharide in the absence of additional substrates. This newly found activity (designated “cellulose endotransglucosylase,” or CET) can potentially be involved in the formation of covalent linkages between cellulose microfibrils in the plant cell wall. It can also comprise a new route of industrial cellulose functionalization.

Mitigation of ovalbumin glycation in vitro by its treatment with green tea polyphenols

Polyphenols are known as inhibitors of glycation since they alter the pathways of the Maillard reaction by several mechanisms involving antioxidant activity, reactive dicarbonyl trapping, inhibition of sugar autoxidation, and amino group binding. Green tea is a rich source of polyphenols. This study aimed to investigate the effects of protein modification with green tea polyphenols on glycation potential of ovalbumin. For this purpose, green tea infusion was prepared and ovalbumin was treated with that infusion at alkaline pH conditions in order to let oxidation of polyphenols to quinone forms and formation of covalent linkages between quinones and amine residues of protein. This modified ovalbumin was heated with glucose at 90 °C. Furosine, the compound formed from N-e-fructoselysine during acid hydrolysis, and N-e-carboxymethyl lysine (CML) as indicators of early and advanced glycation, respectively, were monitored. Free lysine concentrations and antioxidant activity were measured in order to enlighten the interaction mechanism. Results showed that treatment of ovalbumin with green tea phenolics before reaction with glucose has a potential to limit glycation. In total 15 % less furosine was formed in treated ovalbumin than control ovalbumin upon heating at 90 °C for 1 h, whereas 14 % less CML was formed.