The Mechanism of Carotenoid Degradation in Flue-Cured Tobacco and Changes in the Related Enzyme Activities at the Leaf-Drying Stage During the Bulk Curing Process

The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical basis for optimization of curing technology. The effect of different rising speeds of temperature on the carotenoid degradation and the related enzymes activities at the color-fixing stage during the bulk curing process was studied by using the electric-heated fluecuring barn designed by Henan Agricultural University, China, based on curing technology with yellowing at low temperature and moderate humidity and leaf drying at moderate humidity. The results showed that the carotenoid degradation components （β-carotene, lutein, neoxanthin, and violaxthin） decreased gradually at the color-fixing stage during the bulk curing process. The carotenoid degradation components viz.,β-carotene, lutein, neoxanthin, and violaxthin at the slow heating curing （T1） were relatively higher than the rapid heating curing （T2） accounting for 10, 2, 32 and 32% respectively, but there were no differences among treatments （P〉 0.05）. The effect of different conditions of curing on the activities of enzymes related to carotenoids degradation were significant. The lipoxygenase, phenylalanine ammonialyase, peroxidase, and polyphenol oxidase enzymes had a bidirectional effect on the quality of tobacco leaves and it was beneficial to form more premise matter of aroma based on the higher enzyme activities at the early leaf-drying stage. The slow heating could regulate the change in various enzymes＇ activities reasonably, making cell redox reaction to reach the dynamic balance and make the degradation of carotenoids adequately. Meanwhile, it could avoid the occurrence of browning reaction and provide foundation for improving the quality of tobacco and optimization of technology for bulk curing and further enhancing aroma.

Enzyme‐like mechanism of selective toluene oxidation to benzaldehyde over organophosphoric acid‐bonded nano‐oxides

The completely selective oxidation of toluene to benzaldehyde with dioxygen,without the need touse H_(2)O_(2),halogens,or any radical initiators,is a reaction long desired but never previously successful.Here,we demonstrate the enzyme‐like mechanism of the reaction over hexadecylphosphateacid(HDPA)‐bonded nano‐oxides,which appear to interact with toluene through specific recognition.The active sites of the catalyst are related to the ability of HDPA to change its bonding to theoxides between monodentate and bidentate during the reaction cycle.This greatly enhances themobility of the crystal oxygen or the reactivity of the catalyst,specifically in toluene transformations.The catalytic cycle of the catalyst is similar to that of methane monooxygenase.In thepresence of catalyst and through O_(2)oxidation,the conversion of toluene to benzaldehyde is initiatedat 70°C.We envision that this novel mechanism reveals alternatives for an attractive route to designhigh‐performance catalysts with bioinspired structures.

Relevant Enzymes, Genes and Regulation Mechanisms in Biosynthesis Pathway of Stilbenes

Stilbenes are natural phenolic compounds which function as antimicrobial phytoalexins in plants and affect human health as cardioprotective, antibaceteria, antioxidative and antineoplastic agents. In this review, the progresses of study on relevant enzymes, genes, and regulation mechanism in biosynthesis pathway of stilbenes are described. Here we introduce a holistic and systematic method of researching relevant enzymes, genes and other regulatory factors in biosynthesis pathway of stilbenes—Systems biology. The application of knowledge of relative enzymes, genes and regulation mechanisms in stilbenes biosynthesis in metabolic engineering which is used as a tool of improving the disease resistance of plants and health caring quality of crops is also discussed.

Application of Enzyme Inhibition Therapy in the Management/Treatment of Neurological Conditions, Diseases, and Disorders

Enzyme inhibition therapy uses specific molecules to inhibit enzyme activity, targeting disease-related enzymes in medical treatments like cancer treatment and infectious disease management. Different types of inhibitors, competitive and non-competitive, bind to different sites and alter enzyme function. The success of this therapy depends on the inhibitor’s specificity and delivery to the target site. Further research could lead to more effective treatments. Nowadays, the majority of medications are enzyme inhibitors and are in the clinical or pre-clinical stages of drug development. Enzyme inhibitors are often prescribed medications for a variety of illnesses, including neurological problems. There is only symptomatic therapy available for many neurological conditions, particularly neuro-degenerative disorders, as opposed to therapy based on knowledge of the underlying mechanisms of these diseases. Enzyme inhibitors are useful as they block the function of certain enzymes whose aberrant activity could be contributing to the illness. They also alleviate the symptoms and stop the disease’s progression. This review discusses the mechanism of action of several enzyme inhibitors that have been prescribed as medications for neurological illnesses as well as some that are still in research stages.

Mechanism and Application of Enzyme Treatment on Wool

Protease treatments on wool have its inherent defect in shrink-proofing because protease will decompose wool through cell membrane complex （CMC）. In order to solve this problem, mechanism of enzyme treatments on wool was adequately analyzed and possible enzyme applications were discussed. The mechanism of enzyme treatment on wool was analyzed through weight loss, strength, scanning electron microscopy （SEM）, electrophoresis, sodium dodecyl sulfate polyacrylamide gel electrophoresis （ SDS- PAGE）, and amino acids composition. Based on the results, a possible novel multifunetional enzyme treatment on wool to achieve shrink-resistance was proposed. In order to shorten enzyme treatment time, the rate of proteolysis of wool was investigated. Considering the specificity of proteases, wool composition, and structure of dyes, a better enzyme pretreatment before dyeing to get better dyeabflity and lower dyeing temperature was discussed.

Food-derived bio-functional peptides for the management of hyperuricemia and associated mechanism

Hyperuricemia,a metabolic disorder related to uric acid metabolism dysregulation,has become a common metabolic disease worldwide,due to changes in lifestyle and dietary structure.In recent years,owing to their high activity and few adverse effects,food-derived active peptides used as functional foods against hyperuricemia have attracted increasing attention.This article aims to focus on the challenge associated with peptide-specific preparation methods development,functional components identification,action mechanism(s)clarification,and bioavailability improvement.The current review proposed recent advances in producing the food-derived peptides with high anti-hyperuricemia activity by protein source screening and matched enzymatic hydrolysis condition adjusting,increased the knowledge about strategies to search antihyperuricemia peptides with definite structure,and emphasized the necessity of combining computer-aided approaches and activity evaluations.In addition,novel action mechanism mediated by gut microbiota was discussed,providing different insights from classical mechanism.Moreover,considering that little attention was paid previously on the structure-activity relationships of anti-hyperuricemia peptides,we collected the sequences from published studies and make a preliminary summary about the structure-activity relationships,which in turn provided guides for enzymatic hydrolysis optimization and bioavailability improvement.Hopefully,this article could promote the development,application and commercialization of food-derived anti-hyperuricemia peptides in the future.

Effects of mechanical damage and herbivore wounding on H2O2 metabolism and antioxidant enzyme activities in hybrid poplar leaves

The changes of hydrogen peroxide （H2O2） metabolism and antioxidant enzyme activities in a hybrid poplar （Populus simonii xp. pyramidalis ＇Opera 8277＇） in response to rnechanical damage （MD） and herbivore wounding （HW） were investigated to determine whether H2O2 could function as the secondary messenger in the signaling of systemic resistance. Results show that H2O2 was generated in wounded leaves through MD and HW treatments and systemically in unwounded leaves around the wounded leaves. The activities of antioxidant enzymes such as superoxide dismutase （SOD）, catalase （CAT） and ascorbate peroxidase （APX） were also enhanced. However, the H2O2 accumulation and antioxidant enzyme activities were inhibited in MD leaves through the pretreatment with DPI （which is a specific inhibitor of NADPH oxidase）. The results of this study suggest that H2O2 could be systemically induced by MD and HW treatments, and H2O2 metabolism was closely related to the change in SOD, APX and CAT activities. A high level of antioxidant enzymes could decrease membrane lipid peroxidation levels and effectively induce plant defense responses.

Antioxidant Protection Mechanisms Reveal Significant Response in Drought-Induced Oxidative Stress in Some Traditional Rice of Assam, India

Drought tolerance levels and antioxidant protection mechanisms were evaluated for 21 traditional rice varieties of Assam, India, along with Sahbhagi Dhan （drought tolerant） and IR64 （drought sensitive） as controls. Drought was imposed in hydroponic culture with polyethylene glycol 6000 （PEG6000） that was initially standardized with different concentrations. All the rice varieties showed apparent decreases in growth characteristics under drought stress （initially at 15% for 7 d followed by 20% PEG6000 for 7 d in Yoshida medium）. On the basis of standard evaluation score （SES）, eight rice varieties showed high drought tolerance which were carried forward for further biochemical analyses. Based on different morpho- physiological parameters, SN03 （Bora）, SN04 （Prosad Bhog）, SN05 （Kola Joha）, SN06 （Helash Bora）, SN08 （Salihoi Bao）, SN12 （Kola Amona）, SN20 （Ronga Bora） and SN21 （Sok-Bonglong） were identified as promising drought tolerant varieties. The non-enzymatic antioxidants activities viz., glutathione, ascorbate and enzymatic antioxidant activities such as superoxide dismutase （SOD）, catalase （CAT）, guaiacol peroxidase （GPX）, ascorbate peroxidase （APX）, glutathione reductase （GR） in shoots and roots of all the selected varieties revealed significant level of protection mechanisms as compared with controls. Enhancement in activities of the overall antioxidant enzymes including SOD, GPX, CAT, GR and APX under drought stress reflects their role in the adaptation process under water stress.

Effects of Terpinen-4-ol on Four Metabolic Enzymes and Polyphenol Oxidase (PPO) in Mythimna separta Walker

To study insecticidal mechanism of terpinen-4-ol, a main insecticidal composition in the essential oil of Sabina vulgaris, the 5th instar larvae of Mythimna separta, were investigated with terpinen-4-ol by topical application. The activities of phosphatase, glutathione S-transferase （GSTs）, cytochrome P450 （P450）, and polyphenol oxidase （PPO） of tested insects were determined in all poisoning stages, including exciting stage, convulsing stage, paralysis stage, and recover stage. The result showed that the activities of both acid phosphatase （ACP） and alkaline phosphatase （AKP） in treated insects were induced by terpinen-4-ol, but ACP was inhibited in paralysis stage. The activities of GSTs were inhibited in exciting stage, convulsing stage, and paralysis stage, but gradually recovered in recover stage. O-demethylase activity of cytochrome P450 was inhibited by terpinen-4-ol, and the inhibition rate in all poisoning stages were 26.27, 46.03, 80.24, and 90.22%, respectively. PPO activities were strongly inhibited by terpinen-4-ol both in vitro and in vivo. In conclusion, the activities of P450, GSTs, and PPO could have relation with toxicity of terpinen-4-ol against larvae of the Mythimna separta, but recover stage of the poisoning insects might be related to GSTs induced. As a new insecticide or synergist, terpinen- 4-ol has a potential value in field of insecticide resistance management.

Diversity of the reaction mechanisms of SAM-dependent enzymes

S-adenosylmethionine(SAM) is ubiquitous in living organisms and is of great significance in metabolism as a cofactor of various enzymes. Methyltransferases(MTases), a major group of SAMdependent enzymes, catalyze methyl transfer from SAM to C, O, N, and S atoms in small-molecule secondary metabolites and macromolecules, including proteins and nucleic acids. MTases have long been a hot topic in biomedical research because of their crucial role in epigenetic regulation of macromolecules and biosynthesis of natural products with prolific pharmacological moieties. However, another group of SAM-dependent enzymes, sharing similar core domains with MTases, can catalyze nonmethylation reactions and have multiple functions. Herein, we mainly describe the nonmethylation reactions of SAMdependent enzymes in biosynthesis. First, we compare the structural and mechanistic similarities and distinctions between SAM-dependent MTases and the non-methylating SAM-dependent enzymes. Second,we summarize the reactions catalyzed by these enzymes and explore the mechanisms. Finally, we discuss the structural conservation and catalytical diversity of class I-like non-methylating SAM-dependent enzymes and propose a possibility in enzymes evolution, suggesting future perspectives for enzymemediated chemistry and biotechnology, which will help the development of new methods for drug synthesis.

Chromium detoxification mechanism induced growth and antioxidant responses in vetiver(Chrysopogon zizanioides(L.) Roberty)

This study investigated the chromium(Cr)detoxification mechanism-induced changes in growth and antioxidant defence enzyme activities in Chrysopogon zizanioides.Plant growth decreased by 36.8%and 45.0%in the shoots and roots,respectively,in the 50 mg/L Cr treatment.Cr accumulation was higher in root(9807μg/g DW)than in shoots(8730μg/g DW).Photosynthetic pigments and malondialdehyde content increased up to the 30 mg/L Cr treatment,whereas they declined at higher doses.The activity of superoxide dismutase(SOD),catalase(CAT)and peroxidase(POX)were increased significantly with increasing of Cr dose but slightly declined at higher doses.Isozyme banding patterns revealed the expression of multiple bands for SOD,CAT and POX enzymes,and the band intensity decreased at high doses of Cr exposure.These results indicate that higher Cr doses increased the oxidative stress by over production of reactive oxygen species(ROS)in vetiver that had potential tolerance mechanism to Cr as evidenced by enhanced level of antioxidative enzymes,photosynthetic pigments,MDA contents.Therefore,vetiver has evolved a mechanism for detoxification and accumulates higher concentration of toxic Cr.This study provides a better understanding of how vetiver detoxifies Cr.

Theoretical Study on GSH Activation Mechanism of a New Type of Glutathione Transferase Gtt2

Glutathione transferases（GSTs） play an important role in the detoxification of xenobiotic/endobiotic toxic compounds. The α-, π-, and/l-classes of cytosolic GSTs have been studied extensively, while Gtt2 from Saccharo- myces cerevisiae, a novel atypical GST, is still poorly understood. In the present study, we investigated the gluta- thione（GSH） activation mechanism of Gtt2 using the density functional theory（DFT） with the hybrid functional B3LYP. The computational results show that a water molecule could assist a proton transfer between the GSH thiol and the N atom of His133. The energy barrier of proton transfer is 46.0 kJ/mol. The GSH activation mechanism and the characteristics of active site are different from those of classic cytosolic GSTs.

HOMOGENIZATION RESULTS FOR ENZYME CATALYZED REACTIONS THROUGH POROUS MEDIA

The aim of this article is to study the effective behavior of the solution of a nonlinear problem arising in the modelling of enzyme catalyzed reactions through the exterior of a domain containing periodically distributed reactive solid obstacles,with period ε.The asymptotic behavior of the solution of such a problem is governed by a new elliptic boundary-value problem,with an extra zero-order term that captures the effect of the enzymatic reactions.

Limited distribution and mechanism of the TetX4 tetracycline resistance enzyme

Tetracyclines,a group of antimicrobial agents targeting protein synthesis,have been extensively used in agricultural,veterinary,and clinic settings[1].The sporadic rise in tetracycline resistance is partially due to the occurrence of efflux pumps and/or ribosome protection[1,2].The growing body of tetracycline-inactivating enzymes(e.g.,TetX(X1 to X4)[3,4]and Tet(47 to 55)[5])represents an alternative mechanism for tetracycline resistance,and threatens the renewed interest of tigecycline as a last-resort defense against lethal infections with carbapenem-resistant Enterobacteriaceae and Acinetobacter species.

Effects of mechanical damage and herbivore wounding on H_2O_2 metabolism and antioxidant enzyme activities in hybrid poplar leaves

The changes of hydrogen peroxide(H2O2) metabolism and antioxidant enzyme activities in a hybrid poplar(Populus simonii ×P.pyramidalis ‘Opera 8277') in response to mechanical damage(MD) and herbivore wounding(HW) were investigated to determine whether H2O2 could function as the secondary messenger in the signaling of systemic resistance.Results show that H2O2 was generated in wounded leaves through MD and HW treatments and systemically in unwounded leaves around the wounded leaves.The activities of antioxidant enzymes such as superoxide dismutase(SOD), catalase(CAT) and ascorbate peroxidase(APX) were also enhanced.However, the H2O2 accumulation and antioxidant enzyme activities were inhibited in MD leaves through the pretreatment with DPI(which is a specific inhibitor of NADPH oxidase).The results of this study suggest that H2O2 could be systemically induced by MD and HW treatments, and H2O2 metabolism was closely related to the change in SOD, APX and CAT activities.A high level of antioxidant enzymes could decrease membrane lipid peroxidation levels and effectively induce plant defense responses.

Molecular mechanism prediction analysis of compound Kushen injection in the treatment of COVID-19 based on network pharmacology and molecular docking

Background:As one of the eight effective traditional Chinese medicines for the treatment of atypical pneumonia,compound Kushen injection(CKI)played an important role in combating pneumonia caused by severe acute respiratory syndrome coronavirus 2 virus in China in 2003.CKI is known to inhibit inflammation,and its main chemical components,namely matrine and oxymatrine,can promote Th cells to recognize and eliminate viruses.In this study,network pharmacology and molecular docking were used to explore the mechanisms of CKI for treating coronavirus disease 2019.Methods:The Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform and other related literature were used to screen CKI’s active ingredients in the blood.Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform,Swiss Target Prediction and STITCH were used to search for potential targets of the active ingredients.The“ingredient-target”network was constructed using the Cytoscape software.The STRING online database was used to construct a target protein-protein interaction network that can be visualized and analyzed using the Cytoscape software to obtain key targets.Results:Sophocarpine,sophoridine,matrine,(+)-allomatrine,AIDS211310,and sophranol were the six active ingredients.After docking the active ingredients with severe acute respiratory syndrome coronavirus 23CL hydrolase and angiotensin-converting enzyme 2(ACE2),they displayed suitable affinity,which could block viral replication and its binding to ACE2.The key targets mainly involved inflammatory factors,such as interleukin-6(IL-6)and tumor necrosis factor(TNF).Gene Ontology enrichment analysis mainly indicated the IL-6 cytokine-mediated signaling pathway and cytokine-mediated signaling pathway.The Kyoto Encyclopedia of Genes and Genome pathway enrichment analysis mainly indicated steroid hormone biosynthesis and the TNF signaling pathway.Conclusion:The alkaloids in CKI can block viral replication and its binding to severe acute respiratory syndrome coronavirus 2 and ACE2 receptors.They regulate the IL-6-mediated signaling pathway,TNF signaling pathway,and steroid hormone biosynthesis,thereby initiating therapeutic responses against coronavirus disease 2019.

Physiological mechanisms involved in resistance to cotton verticillium wilt induced by AM fungi

It was proved that arbuscular mycorrhizal (AM) fungi played an important role in increasing plant resistance to soilborne pathogens, especially when plants were pre-inoculated with AM fungi. Mechanisms involved in this phenomenon are not yet well understood. On the basis of the former experiment results in our lab, effects of AM fungi on cotton Verticillium wilt and the mechanisms of increasing disease resisitance by the tested fungi were studied in pot culture under greenhouse conditions. Two cotton cutivars Litai 8 and 86-1 which are susceptible to Verticillium dahliae were pre-inoculated with Glomus fasiculatum, and Gigaspora margarita, then inoculated with the strain of Verticillium dahliae, namely “An-Yang” (belong to intermediate virulent type) 30 days after the former inoculation. Results showed that AM fungi could improve the growth and development of cotton plants, increase plants dry mass, decrease incidence and disease index of Verticillium wilt of cotton plants, inhibit the infection and development of V. dahliae to different extent in the rhizosphere of cotton pre-inoculated with AM fungi, while the colonization and spore numbers of AM fungi were not reduced significantly by this pathogen. The defence enzymes, such as phenylalanine ammonia-lyase (PAL), chitinase, β-1,3-glucanase, peroxidase, polyphenoloxidase (PPO) were induced, and their activities and peak increased by AM fungi in roots and leaves, and the increasing speed and peak of the enzyme activity were higher in treatment with AM fungus preinoculation than the inoculation with only V. dahliae, which suggested that defense response was activated by AM fungi, and then made the cotton to react strongly and rapidly to the infection of V. dahliae. In addition, AM fungi decreased the content of malondiadehyde (MDA) in cotton roots and leaves, protected membrane system and alleviated the damage caused by the pathogen. The AM fungus, Glomus fasiculatum showed the superior effects of biological control. It was concluded that AM fungi could provide the biological control to cotton diseases and there were application prospects of this biological agents.

HOMOGENIZATION RESULTS FOR ENZYME CATALYZED REACTIONS THROUGH POROUS MEDIA

The aim of this article is to study the effective behavior of the solution of a nonlinear problem arising in the modelling of enzyme catalyzed reactions through the exterior of a domain containing periodically distributed reactive solid obstacles,with period ε.The asymptotic behavior of the solution of such a problem is governed by a new elliptic boundary-value problem,with an extra zero-order term that captures the effect of the enzymatic reactions.

D-band center coordination modulated enzyme-like activity in Fe-Cu dual-metal single-atom nanozymes

After explorations in a diversity of single-atom nanozymes(SAzymes),developing dual-centered SAzymes becomes a promising approach for superior catalytic performance.But confusing mechanisms including atomic coordination,spatial configuration,and metal–metal atom interaction hinder the development and design of SAzymes.Herein,a dual-centered Fe-Cu-N_(x)SAzyme exhibits excellent peroxidase(POD)-and catalase(CAT)-like activities with d-band center(ε_(d))coordination of Fe and Cu in multiple reaction stages,which plays a critical role in the adsorption of H_(2)O_(2)molecule and H_(2)O and O_(2)release.Therefore,the dband center coordination,which can be represented byε_(d)(Fe)–ε_(d)(Cu)shifts,leads to the competition between one-side and bilateral adsorption,which determines the favorable reaction path with lower energy barriers.Based on experimental statistics,simulated formation energies,and reaction barriers,3 configurations,Fe-Cu-N6-I,Fe-Cu-N_(8)-II,and Fe-Cu-N_(8)-III,are modeled and validated.Impressively,configuration-dependent catalytic selectivity and the competition between one-side and bilateral adsorption can be unveiled by d-band center coordination paradigm analysis.Theoretical simulations suggest that the unsymmetrical charge distribution over the three Fe-Cu configurations could tune the adsorption strength compared with the counterparts FeN_(4)and CuN_(4).The present work provides a potential route for optimizing enzyme-like catalysis by designing the dual-or even triple-metal SAzymes,which demonstrates the large space to modulate the metal atomic configuration and interaction.

Mechanisms by which microbial enzymes degrade four mycotoxins and application in animal production:A review

Mycotoxins are toxic compounds that pose a serious threat to animal health and food safety.Therefore,there is an urgent need for safe and efficient methods of detoxifying mycotoxins.As biotechnology has continued to develop,methods involving biological enzymes have shown great promise.Biological enzymatic methods,which can fundamentally destroy the structures of mycotoxins and produce degradation products whose toxicity is greatly reduced,are generally more specific,efficient,and environmentally friendly.Mycotoxin-degrading enzymes can thus facilitate the safe and effective detoxification of mycotoxins which gives them a huge advantage over other methods.This article summarizes the newly discovered degrading enzymes that can degrade four common mycotoxins(aflatoxins,zearalenone,deoxynivalenol,and ochratoxin A)in the past five years,and reveals the degradation mechanism of degrading enzymes on four mycotoxins,as well as their positive effects on animal production.This review will provide a theoretical basis for the safe treatment of mycotoxins by using biological enzyme technology.