Hydrolysis Of Chains Research Articles

Tailoring flexibility and dispersity of thermoplastic starch gel by controlling intermolecular structure for improving folding endurance of polylactide

• A biobased starch gel with high thermoplasticity was fabricated via reactive extrusion. • For the first time, we characterized and defined this thermoplastic starch as gel, instead of plastic. • A novel “Soft-Hard” structure provided by tartaric acid endowed TGTPS gel with better flexibility. • TGTPS-1 gel acted as micro/nano-meter toughener and motivated PLA to achieve outstanding folding endurance. Polysaccharide-based gels are green, non-toxic, and sustainable materials with a high absorption capability, which make them suitable for numerous applications. In this study, a novel starch-based thermoplastic gel (TGTPS gel) was facilely fabricated via reactive extrusion with glycerol, starch and tartaric acid. The TGTPS gels exhibited tremendous increase of flexibility and processability, which was attributed to the fact that TA molecules could facilitate hydrolysis of starch chains and enhance gel network slippage as evident from gel permeation chromatography and stress-relaxation measurement. Moreover, combining dynamic mechanical analysis and rheological behavior, we found that a special Soft-Hard Segments structure, varied with the fluctuation of tartaric acid (TA) concentration, was developed between TA molecules, glycerol and starch chains. Additionally, TGTPS gels with 1% TA content (TGTPS-1) could also serve as micro/nano-meter toughener, and motivate PLA to achieve outstanding folding endurance. The double folding resistance was performed on PLA/TGTPS-1 blend, and folding cycle time was improved from 1 time of PLA to over 2000 times of PLA/TGTPS-1 (80/20) blends. Overall, this novel TGTPS gels could be promising alternative to petroleum-based polymers and play a great potential in engineering applications.

Emerging Roles of Ubiquitin-Specific Protease 25 in Diseases.

The balance of ubiquitination and deubiquitination plays diverse roles in regulating protein stability and cellular homeostasis. Deubiquitinating enzymes catalyze the hydrolysis and removal of ubiquitin chains from target proteins and play critical roles in various disease processes, including cancer, immune responses to viral infections and neurodegeneration. This article aims to summarize roles of the deubiquitinating enzyme ubiquitin-specific protease 25 (USP25) in disease onset and progression. Previous studies have focused on the role of USP25 in antiviral immunity and neurodegenerative diseases. Recently, however, as the structural similarities and differences between USP25 and its homolog USP28 have become clear, mechanisms of action of USP25 in cancer and other diseases have been gradually revealed.

Integrated Multi-omics Investigations Reveal the Key Role of Synergistic Microbial Networks in Removing Plasticizer Di-(2-Ethylhexyl) Phthalate from Estuarine Sediments.

ABSTRACTDi-(2-ethylhexyl) phthalate (DEHP) is the most widely used plasticizer worldwide, with an annual global production of more than 8 million tons. Because of its improper disposal, endocrine-disrupting DEHP often accumulates in estuarine sediments in industrialized countries at submillimolar levels, resulting in adverse effects on both ecosystems and human beings. The microbial degraders and biodegradation pathways of DEHP in O2-limited estuarine sediments remain elusive. Here, we employed an integrated meta-omics approach to identify the DEHP degradation pathway and major degraders in this ecosystem. Estuarine sediments were treated with DEHP or its derived metabolites, o-phthalic acid and benzoic acid. The rate of DEHP degradation in denitrifying mesocosms was two times slower than that of o-phthalic acid, suggesting that side chain hydrolysis of DEHP is the rate-limiting step of anaerobic DEHP degradation. On the basis of microbial community structures, functional gene expression, and metabolite profile analysis, we proposed that DEHP biodegradation in estuarine sediments is mainly achieved through synergistic networks between denitrifying proteobacteria. Acidovorax and Sedimenticola are the major degraders of DEHP side chains; the resulting o-phthalic acid is mainly degraded by Aestuariibacter through the UbiD-dependent benzoyl coenzyme A (benzoyl-CoA) pathway. We isolated and characterized Acidovorax sp. strain 210-6 and its extracellular hydrolase, which hydrolyzes both alkyl side chains of DEHP. Interestingly, genes encoding DEHP/mono-(2-ethylhexyl) phthalate (MEHP) hydrolase and phthaloyl-CoA decarboxylase—key enzymes for side chain hydrolysis and o-phthalic acid degradation, respectively—are flanked by transposases in these proteobacterial genomes, indicating that DEHP degradation capacity is likely transferred horizontally in microbial communities.IMPORTANCE Xenobiotic phthalate esters (PAEs) have been produced on a considerably large scale for only 70 years. The occurrence of endocrine-disrupting di-(2-ethylhexyl) phthalate (DEHP) in environments has raised public concern, and estuarine sediments are major DEHP reservoirs. Our multi-omics analyses indicated that complete DEHP degradation in O2-limited estuarine sediments depends on synergistic microbial networks between diverse denitrifying proteobacteria and uncultured candidates. Our data also suggested that the side chain hydrolysis of DEHP, rather than o-phthalic acid activation, is the rate-limiting step in DEHP biodegradation within O2-limited estuarine sediments. Therefore, deciphering the bacterial ecophysiology and related biochemical mechanisms can help facilitate the practice of bioremediation in O2-limited environments. Furthermore, the DEHP hydrolase genes of active DEHP degraders can be used as molecular markers to monitor environmental DEHP degradation. Finally, future studies on the directed evolution of identified DEHP/mono-(2-ethylhexyl) phthalate (MEHP) hydrolase would bring a more catalytically efficient DEHP/MEHP hydrolase into practice.

Dispersion, fluidity retention and retardation effect of polyacrylate-based ether superplasticizer nanomicelles in Portland cement

The superplasticizers with a high-order configuration including star, branched, clawed or corosslinked shape, have exhibited superior fluidity retention effect in cementitious mixes, but are often prepared with tedious routes. This paper employed a facile and proven emulsion polymerization technology to prepare nanomicellar polyacrylate ether superplasticizer (PAE). The precise tri-copolymer structure of PAE of poly(tert-butyl acrylate)–co-polycarboxylate-co-poly(isoprenyl polyethenoxy ether) (PtBA-co-PAA-co-PTPEG) was confirmed by 1H nuclear magnetic resonance (NMR). High-resolution transmission electron microscopy (TEM) verified the core–shell configuration of PAE and further measured colloidal nanomicelles had an average size diameter at 18–35 nm. Based on the special configuration, masses of carboxyl groups were pre-reserved in nanocores via PtBA and encapsulated PAA segments, which would be released into the paste to disperse cement particles over 4 h, during the hydrolysis of PtBA pendent chains and dissociation of nanomicelles. This process was revealed by time-dependent evaluation of spread flow and Zeta potential. Furthermore, the action mechanism of micellar PAE dispersing cement and hydrate by adsorbing onto their surfaces was directly observed by TEM testing. The retardation effect of PAE in Portland cement was evaluated by the delayed hydration heat, lower hydration rate and longer setting time, in comparison with control sample. This work offers a superior fluidity retention superplasticizer for reducing the fluidity loss of cement paste, and demonstrates the fluidity retention mechanism of colloidal PAE via nanomicelle dissociation, carboxyl release, and redispersion in alkaline cement paste.

Experimental and Theoretical Study on Glycolic Acid Provided Fast Bio/Seawater-Degradable Poly(Butylene Succinate-co-Glycolate)

The very slow degradation of biodegradable polymers in the marine environment is due to the lack of dedicated degradation enzymes in open seas. As a result, introducing monomers that have a fast hydrolysis process is required to accelerate seawater degradation. Poly(butylene succinate-co-glycolate) (PBSGA) copolyesters with glycolic acid (GA) units ranging from 5 to 40% were synthesized by our newly developed polymerizing method based on oligo(glycolic acid). The results of ¹H-NMR and GPC revealed that short GA segments were evenly distributed between BS segments, obtaining random copolyesters with a weight-average molecular weight over 6.24 * 10⁴ g/mol. The copolymerized GA units hinder its crystallization capability and increase hydrophilicity of the PBSGAs, which still displayed mechanical properties comparable or even better than most biodegradable polymers. Fast degradation in seawater and enzymatic environments (Candida antarctica lipase B enzymes) is proved experimentally. The quick decomposition in seawater was originated from accelerated hydrolysis. For instance, the weight loss of PBSGA40 (compositions of GA units) exceeded 22% after 49 days. Possible degradation mechanisms were proposed based on Fukui function analysis and frontier molecular orbital calculation. Additionally, the energy barrier for hydrolysis was calculated by the density functional theory method, indicating that the hydrolysis of the polymer chain became more and more easy with the increase in GA units. At last, the addition of GA units only had a mild effect on the shelf life of the PBSGAs.

DNAzyme Amplified Aptasensing Platform for Ochratoxin A Detection Using a Personal Glucose Meter.

Aptamer-based sensors have emerged as a major platform for detecting small-molecular targets, because aptamers can be selected to bind these small molecules with higher affinity and selectivity than other receptors such as antibodies. However, portable, accurate, sensitive, and affordable detection of these targets remains a challenge. In this work, we developed an aptasensing platform incorporating magnetic beads and a DNAzyme for signal amplification, resulting in high sensitivity. The biosensing platform was constructed by conjugating a biotin-labeled aptamer probe of small-molecular targets such as toxins and a biotin-labeled substrate strand on magnetic beads, and the DNAzyme strand hybridized with the aptamer probe to block the substrate cleavage activity. The specific binding of the small-molecular target by the aptamer probe can replace the DNAzyme strand and then induce the hybridization between the DNAzyme strand and substrate strand, and the iterative signal amplification reaction of hydrolysis and cleavage of the substrate chain occurs in the presence of a metal ion cofactor. Using invertase to label the substrate strand, the detection of small molecules of the toxin is successfully transformed into the measurement of glucose, and the sensitive analysis of small molecules such as toxins can be realized by using the household portable glucose meter as a readout. This platform is shown to detect ochratoxin, a common toxin in food, with a linear detection range of 5 orders of magnitude, a low detection limit of 0.88 pg/mL, and good selectivity. The platform is easy to operate and can be used as a potential choice for quantitative analysis of small molecules, at home or under point-of-care settings. Moreover, by changing and designing the aptamer probe and the arm of DNAzyme strand, it can be used for the analysis of other analytes.

Proteasome interaction with ubiquitinated substrates: from mechanisms to therapies.

The 26S proteasome is responsible for regulated proteolysis in eukaryotic cells. Its substrates are diverse in structure, function, sequence length, and amino acid composition, and are targeted to the proteasome by post-translational modification with ubiquitin. Ubiquitination occurs through a complex enzymatic cascade and can also signal for other cellular events, unrelated to proteasome-catalyzed degradation. Like other post-translational protein modifications, ubiquitination is reversible, with ubiquitin chain hydrolysis catalyzed by the action of deubiquitinating enzymes (DUBs), ~90 of which exist in humans and allow for temporal events and dynamic ubiquitin-chain remodeling. DUBs have been known for decades to be an integral part of the proteasome, as deubiquitination is coupled to substrate unfolding and translocation into the internal degradation chamber. Moreover, the proteasome also binds several ubiquitinating enzymes and shuttle factors that recruit ubiquitinated substrates. The role of this intricate machinery and how ubiquitinated substrates interact with proteasomes remains an area of active investigation. Here, we review what has been learned about the mechanisms used by the proteasome to bind ubiquitinated substrates, substrate shuttle factors, ubiquitination machinery, and DUBs. We also discuss many open questions that require further study or the development of innovative approaches to be answered. Finally, we address the promise of expanded therapeutic targeting that could benefit from such new discoveries.

Characterization and in vitro digestion properties of cassava starch and epigallocatechin-3-gallate (EGCG) blend

In this study, characteristics and in vitro digestibility of cassava starch and epigallocatechin-3-O-gallate (EGCG) blend were investigated. The structure changes of the starch during digestion were also evaluated. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) revealed that starch-EGCG blend had more ordered crystal structure and stronger thermal stability as compare to the native starch. Iodine binding analysis suggested the incorporation of starch and EGCG. Starch-EGCG blend retained strong ability of DPPH radical scavenging after storage, indicating that starch could protect EGCG from oxidation. EGCG greatly inhibited the enzymatic hydrolysis of starch during digestion, and the starch could keep EGCG controlled-released. The addition of EGCG decreased the rate of granule collapse and molecular weight reduction of the starch during digestion. The hydrolysis of long and medium length chains of the starch was restrained greatly, and the short chains were protected from hydrolyzing by blending with EGCG during digestion.

Insight into the Effects of Sous Vide on Cathepsin B and L Activities, Protein Degradation and the Ultrastructure of Beef.

This study aimed to evaluate the effects of sous vide cooking (SV) on beef tenderness and its underlying potential mechanism. Beef semimembranosus (SM) were subjected to SV treatments at 45 °C, 55 °C and 65 °C for 4 h. Compared with control samples (CK, cooked at 75 °C until a core temperature of 72 °C was attained), SV treatment significantly promoted the release of cathepsin B and cathepsin L from lysosomes and decreased the shear force of beef SM (p < 0.05). In comparison with CK, samples treated with SV had more hydrolysis of myosin heavy chain and obtained higher myofibrillar fragmentation index, collagen solubility as well as longer sarcomere length (p < 0.05). The current study showed that the proteolysis of myofibrillar protein and collagen induced by cathepsin B and cathepsin L, and the limited longitudinal shrinkage together contributed to the improvement of beef tenderness upon SV.

Accelerated degradation of HAP/PLLA bone scaffold by PGA blending facilitates bioactivity and osteoconductivity

The incorporation of hydroxyapatite (HAP) into poly-l-lactic acid (PLLA) matrix serving as bone scaffold is expected to exhibit bioactivity and osteoconductivity to those of the living bone. While too low degradation rate of HAP/PLLA scaffold hinders the activity because the embedded HAP in the PLLA matrix is difficult to contact and exchange ions with body fluid. In this study, biodegradable polymer poly (glycolic acid) (PGA) was blended into the HAP/PLLA scaffold fabricated by laser 3D printing to accelerate the degradation. The results indicated that the incorporation of PGA enhanced the degradation rate of scaffold as indicated by the weight loss increasing from 3.3% to 25.0% after immersion for 28 days, owing to the degradation of high hydrophilic PGA and the subsequent accelerated hydrolysis of PLLA chains. Moreover, a lot of pores produced by the degradation of the scaffold promoted the exposure of HAP from the matrix, which not only activated the deposition of bone like apatite on scaffold but also accelerated apatite growth. Cytocompatibility tests exhibited a good osteoblast adhesion, spreading and proliferation, suggesting the scaffold provided a suitable environment for cell cultivation. Furthermore, the scaffold displayed excellent bone defect repair capacity with the formation of abundant new bone tissue and blood vessel tissue, and both ends of defect region were bridged after 8 weeks of implantation.

A chemical kinetic model for the decomposition of perfluorinated sulfonic acids

Perfluorinated sulfonic acids (such as perfluorooctanesulfonic, PFOS, and short-chain analogues) are notorious halogenated pollutants that exhibit severe toxicity, even at minute levels. Limited number of experimental studies addressed their thermal decomposition at elevated temperatures. Such scenarios are particularly relevant to open fires and incineration of materials laden with perfluoroalkyl compounds (PFCs). Herein, we construct a detail kinetic model that illustrates major chemical reactions underpinning initial degradation of 1-butanesulfonic acid (CF3(CF2)3SO2OH), as a model compound of PFOS, and perfluorinated sulfonic acids in general. Reaction rate parameters were estimated based on an accurate density functional theory (DFT) formalism. The kinetic model incorporates four sets of reactions, namely, unimolecular decomposition channels, hydrofluorination, hydrolysis, and fragmentation of the alkyl chain. Results are discussed considering recent experimental measurements. Temperature-dependent profiles for a large array of perfluoroalkyl acyl fluorides, short perfluorinated cuts, and perfluorinated cyclic compounds, are presented. SO2 emerges as the main sulfur carrier, with a minor contribution from SO3. HF addition to double carbon bonds in alkenes, and to carbonyl bonds in aldehydic structures signifies a major sink pathway for hydrogen fluoride. Addition of moisture was shown to expedite the destruction of relatively large perfluoroalkyl acyl fluorides into C1 species. Construction of this model could aid in a better understanding of the fate and chemical transformation of PFCs under a pyrolytic environment pertinent to waste incineration and fluorine mineralization.

Microstructural Changes during Degradation of Biobased Poly(4-hydroxybutyrate) Sutures.

Fibers of poly(4-hydroxybutyrate) (P4HB) have been submitted to both hydrolytic and enzymatic degradation media in order to generate samples with different types and degrees of chain breakage. Random chain hydrolysis is clearly enhanced by varying temperatures from 37 to 55 °C and is slightly dependent on the pH of the medium. Enzymatic attack is a surface erosion process with significant solubilization as a consequence of a preferent stepwise degradation. Small angle X-ray diffraction studies revealed a peculiar supramolecular structure with two different types of lamellar stacks. These were caused by the distinct shear stresses that the core and the shell of the fiber suffered during the severe annealing process. External lamellae were characterized by surfaces tilted 45° with respect to the stretching direction and a higher thickness, while the inner lamellae were more imperfect and had their surfaces perpendicularly oriented to the fiber axis. In all cases, WAXD data indicated that the chain molecular axis was aligned with the fiber axis and molecules were arranged according to a single orthorhombic structure. A gradual change of the microstructure was observed as a function of the progress of hydrolysis while changes were not evident under an enzymatic attack. Hydrolysis mainly affected the inner lamellar stacks as revealed by the direct SAXS patterns and the analysis of correlation functions. Both lamellar crystalline and amorphous thicknesses slightly increased as well as the electronic contrast between amorphous and crystalline regions. Thermal treatments of samples exposed to the hydrolytic media revealed microstructural changes caused by degradation, with the inner lamellae being those that melted faster.

Progress in K27 ubiquitin modification

Ubiquitination, one type of the most common post-translational modification, mediates the regulation of protein homeostasis in vivo. Since ubiquitin itself contains multiple lysine residues and one N-terminal free amino group, eight types of ubiquitin chains can be formed. The K27 ubiquitin chain is formed through the ubiquitination of the ubiquitin Lys27 (K27), which adopts a compact conformation. In recent years, biological function of the K27 ubiquitin chain in innate immunity, protein homeostasis and DNA damage has been discovered, but the molecular mechanisms of K27 ubiquitin chain assembly, recognition and hydrolysis are still poorly understood. Here we review the structural features and biological functions of K27 ubiquitin chain, to provide a reference for future studies.

A model of polymer degradation and erosion for finite element analysis of bioresorbable implants

Finite element analysis is a powerful tool for the design of bioresorbable medical implants made of aliphatic polyesters such as bioresorbable vascular scaffolds. However polymer erosion has been traditionally modelled using empirical rules rather than differential equations. The rule-based models are difficult to implement in a finite element analysis. Consequently, these models have been limited to simple geometries such as plates or spheres. This paper presents a set of differential equations that govern the hydrolytic chain scission and bulk erosion of bioresorbable implants where polymer erosion is modelled using a differential equation instead of empirical rules. These differential equations can be conveniently solved using a commercial finite element package to calculate the molecular weight and mass loss as functions of time for bioresorbable implant made of aliphatic polyesters. A case study of Absorb bioresorbable vascular scaffolds (BVSs) is presented using data obtained from the literature, where 98 Absorb BVSs were implanted in 40 porcine coronary arteries. It is demonstrated that the finite element model can fit the data of both molecular weight and mass loss as functions of time to an accuracy of approximately 5%. The finite element model and the back-calculated model parameters can be used to design future implants that degrade in a controlled pattern with required mechanical performance.

Influence of Side Chain Hydrolysis on the Evolution of Nanoscale Roughness and Porosity in Amine-Reactive Polymer Multilayers

We report the influence of side chain hydrolysis on the evolution of nanoscale structure in thin films fabricated by the reactive layer-by-layer (LbL) assembly of branched poly(ethylenimine) (PEI) ...

Pectin modifications in raw fruits alter texture of plant cell dispersions

The texture of pureed fruits and vegetables depends primarily on the original tissue structure and cell wall (CW) properties. However, how variations in the raw fruits' cellular and molecular structure determine the rheological behaviour of the purees is little understood, though pectin degradation appears to play a key role. Cultivars, fruit load and post-harvest storage were used to obtain raw apples with different tissue structures, which were processed into purees under simulation of an industrial process. The rheological behaviour of the purees was then compared to particle size, pulp wet mass and serum viscosity. The polysaccharide composition of soluble and insoluble CW material were determined after preparation of alcohol insoluble residue. Macromolecular size and molar mass distributions of soluble pectins were analysed using high performance size-exclusion chromatography coupled to multi-angle laser light scattering and online viscometry. Variations in the raw material, especially induced by post-harvest storage, generated a wide range of different puree's textures. Rheological behaviour of apple purees was driven by particle size, which decreased during prolonged post-harvest storage due to reduced cell adhesion. This was correlated with pectic side chain hydrolysis and modifications in pectin molar mass and structure. Similar trends during storage were observed with different apple cultivars and agricultural practices.

The branched chains and branching degree of exopolysaccharides affecting the stability of anammox granular sludge

The effect of extracellular polysaccharides on the structural stability of granular sludge is widely recognized, and determining their mechanism of action on the stability of granules remains challenging. Herein, enzymatic experiments were used to systematically study the stability changes and internal mechanisms of anammox granular sludge following hydrolysis of extracellular proteins and polysaccharides (PS). The results revealed that the selective hydrolysis of the proteins hardly affected the stability of the granules, while the hydrolysis of the PS branched chains caused the granules to disintegrate. The hydrolysis of the PS chains in the EPS matrix decreased the degree of branching, width and height via nuclear magnetic resonance (NMR) spectroscopy and atomic force microscopy (AFM), and these parameters are closely related to granular stability. Moreover, scanning electron microscopy (SEM) showed a large number of pores and cracks on the granules, bacterial adhesion decreased, and the EPS adhered to the surface of the granules dissolved. The changes in the gel characteristics of the granules were studied by rheology, and the mechanical strength and viscosity of the granular sludge decreased. For the surface characteristics of granules, the zeta potential and hydrophobicity both decreased, revealing that changes in the branched-chain configuration of the PS and the degree of branching caused granular disintegration. Spectral analysis showed that the hydrolysis of the branch points and the branched glycosides of PS led to a higher proportion of hydrophilic and electronegative groups in the EPS matrix, which hindered bacterial aggregation and reduced anammox granule stability. This investigation clarifies the impact of the branched-chain configuration of the PS and their degree of branching on anammox granule stability, which will promote the further application of anammox granules.

Molecular Basis for the Biosynthesis of an Unusual Chain-Fused Polyketide, Gregatin A.

Gregatin A (1) is a fungal polyketide featuring an alkylated furanone core, but the biosynthetic mechanism to furnish the intriguing molecular skeleton has yet to be elucidated. Herein, we have identified the biosynthetic gene cluster of gregatin A (1) in Penicillium sp. sh18 and investigated the mechanism that produces the intriguing structure of 1 by in vivo and in vitro reconstitution of its biosynthesis. Our study established the biosynthetic route leading to 1 and illuminated that 1 is generated by the fusion of two different polyketide chains, which are, amazingly, synthesized by a single polyketide synthase GrgA with the aid of a trans-acting enoylreductase GrgB. Chain fusion, as well as chain hydrolysis, is catalyzed by an α/β hydrolase, GrgF, hybridizing the C11 and C4 carbon chains by Claisen condensation. Finally, structural analysis and mutational experiments using GrgF provided insight into how the enzyme facilitates the unusual chain-fusing reaction. In unraveling a new biosynthetic strategy involving a bifunctional PKS and a polyketide fusing enzyme, our study expands our knowledge concerning fungal polyketide biosynthesis.

Preparation of Starch Citrates Using Solvent Free Reaction and Comparison with Aqueous and Ethanol Mediated Reactions

AbstractCorn starch is modified with citric acid (2.5% w/w) in aqueous, alcoholic media and in solid solid reaction (dry heat condition without any solvent). Degree of substitution is similar for both treatments, independent of use of solvent but higher than for dry heated starch citrate. Apparent amylose content of all starch citrates is higher than for native starch. Molecular weight, as determined by triple detection size exclusion chromatography, also decreases, demonstrating hydrolysis of chains. As a consequence, starch citrate prepared using dry heating and ethanol, as compared to aqueous media, show drastic reduction in pasting viscosity. X‐ray diffraction pattern and morphology of the produced starch granules remain unaltered in all three reaction types. Starch citrates prepared using solvent less reactions show similar characteristics as that of conventional hydrolysis performed using concentrated hydrochloric acid. However, the solid solid hydrolytic reaction process using citric acid is far more environmental friendly and less costly than typical conventional hydrolysis processes. The present study is not only useful for starch systems but more generally for studying reactions in, for example, gums and cellulose.

Intervention on activity and structure of cathepsin L during surimi gel degradation under microwave irradiation

This study was aimed to investigate the effect of microwave heating (MWH) on the activity and conformation of cathepsin L (Cat L) compared to traditional conduction heating during surimi gel degradation stage. The gel properties and SDS-PAGE analysis showed that hydrolysis of myosin heavy chain was prevented by microwave. The activity of Cat L was affected by microwave power and heating time, which inhibited by MWH mainly due to the changes of conductivity caused by the vibration of polar groups under MWH. In addition, the reduction of total sulfhydryl group of Cat L during microwave irradiation led to conformation changes of Cat L. Significant decrease (P < 0.05) in α-helix of Cat L was found using circular dichroism, revealing that MWH altered the secondary structure of Cat L. The molecular chain configuration of Cat L under microwave irradiation was characterized by Laser light scattering. The Rg/Rh of Cat L molecule increased first and then decreased, illustrating that the molecular structure of Cat L was curled up and active center was buried, which lead to the inhibition of Cat L.