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Hydrogen peroxide (H₂O₂) is an important signal molecule involved in plant development and environmental responses. Changes in H₂O₂ availability can result from increased production or decreased metabolism. While plants contain several types of H₂O₂-metabolizing proteins, catalases are highly active enzymes that do not require cellular reductants as they primarily catalyse a dismutase reaction. This review provides an update on plant catalase genes, function, and subcellular localization, with a focus on recent information generated from studies on ARABIDOPSIS: Original data are presented on Arabidopsis catalase single and double mutants, and the use of some of these lines as model systems to investigate the outcome of increases in intracellular H₂O₂ are discussed. Particular attention is paid to interactions with cell thiol-disulphide status; the use of catalase-deficient plants to probe the apparent redundancy of reductive H₂O₂-metabolizing pathways; the importance of irradiance and growth daylength in determining the outcomes of catalase deficiency; and the induction of pathogenesis-related responses in catalase-deficient lines. Within the context of strategies aimed at understanding and engineering plant stress responses, the review also considers whether changes in catalase activities in wild-type plants are likely to be a significant part of plant responses to changes in environmental conditions or biotic challenge.

Metal–organic frameworks (MOFs) have recently garnered consideration as an attractive solid substrate because the highly tunable MOF framework can not only serve as an inert host but also enhance the selectivity, stability, and/or activity of the enzymes. Herein, we demonstrate the advantages of using a mechanochemical strategy to encapsulate enzymes into robust MOFs. A range of enzymes, namely β-glucosidase, invertase, β-galactosidase, and catalase, are encapsulated in ZIF-8, UiO-66-NH 2 , or Zn-MOF-74 via a ball milling process. The solid-state mechanochemical strategy is rapid and minimizes the use of organic solvents and strong acids during synthesis, allowing the encapsulation of enzymes into three prototypical robust MOFs while maintaining enzymatic biological activity. The activity of encapsulated enzyme is demonstrated and shows increased resistance to proteases, even under acidic conditions. This work represents a step toward the creation of a suite of biomolecule-in-MOF composites for application in a variety of industrial processes. Metal–organic frameworks (MOFs) are attractive for encapsulating enzymes for industrial purposes because they can increase selectivity, stability, and/or activity of the enzymes. Here, the authors developed an economical solid-state mechanochemical method to encapsulate enzymes during MOF synthesis.

Table 1 The effects of several interfering chemicals on the activity of the catalase enzyme Supposed chemical interferences Concentration of supposed chemical interferences Added catalase U mL− 1 Found catalase U mL− 1 Relative error (%) Heparin 78.4 USP/10 mL 0.5 0.509 −1.8 EDTA 20.0 μM 0.5 0.511 −2.2 Glucose 0.35 mg mL−1 0.5 0.509 −1.8 Histidine 50 μM 0.5 0.492 1.6 Albumin 0.5 mg mL−1 0.5 0.516 −3.2 Ascorbic acid 20.0 μM 0.5 0.489 2.2 Arginine 50 μM 0.5 0.507 −1.4 Uric Acid 50 μM 0.5 0.495 1 Lysine 50 μM 0.5 0.509 −1.8 The results obtained for each sample by the present assay were compared with those obtained by the dichromate method as described previously by Sinha [7] and modified by Hadwan [8]. Table 4 Analytical recovery of activity of catalase enzyme added to the reaction solution Catalase enzyme contents Catalase enzyme activity added U mL−1 Catalase enzyme calculated activity U mL− 1 Catalase enzyme observed activitya U mL− 1 Recovery % Enzymatic sample – – 5 – Enzymatic sample + catalase enzyme added 1 6 5.85 97.5% Enzymatic sample + catalase enzyme added 3 8 7.9 98.75% Enzymatic sample + catalase enzyme added 5 10 9.82 98.2% Enzymatic sample + catalase enzyme added 7 12 12.11 100.9% Enzymatic sample + catalase enzyme added 8 13 12.75 98.2% Enzymatic sample + catalase enzyme added 9 14 12.7 90.8% Enzymatic sample + catalase enzyme added 10 15 12.75 85% amean of triplicate determinations Conversion of hydrogen peroxide (H2O2) to molecular oxygen and water (H2O) in a chemical reaction regulated by catalase was monitored by determining the absorbance of the carbonato-cobaltate (III) complex as a function of time (as shown in Fig. 2). According to the results shown in Table 1, the presence of vitamins, amino acids, proteins, and antioxidants in biological fluids did not interfere with the currently proposed method of assessing catalase activity. [...]the usual difficulties of the UV-dependent method, including comparatively low selectivity and sensitivity, and disturbance of absorbance due to the evolution of gaseous oxygen, can be overcome.

Hypoxia of solid tumor compromises the therapeutic outcome of photodynamic therapy (PDT) that relies on localized O 2 molecules to produce highly cytotoxic singlet oxygen ( 1 O 2 ) species. Herein, we present a safe and versatile self-assembled PDT nanoagent, i.e., OxgeMCC-r single-atom enzyme (SAE), consisting of single-atom ruthenium as the active catalytic site anchored in a metal-organic framework Mn 3 [Co(CN) 6 ] 2 with encapsulated chlorin e6 (Ce6), which serves as a catalase-like nanozyme for oxygen generation. Coordination-driven self-assembly of organic linkers and metal ions in the presence of a biocompatible polymer generates a nanoscale network that adaptively encapsulates Ce6. The resulted OxgeMCC-r SAE possesses well-defined morphology, uniform size distribution and high loading capacity. When conducting the in situ O 2 generation through the reaction between endogenous H 2 O 2 and single-atom Ru species of OxgeMCC-r SAE, the hypoxia in tumor microenvironment is relieved. Our study demonstrates a promising self-assembled nanozyme with highly efficient single-atom catalytic sites for cancer treatment. The hypoxic microenvironment in solid tumors limits the efficacy of photodynamic therapy (PDT) since oxygen is necessary to produce high cytotoxic singlet oxygen species. Here, the authors develop an improved self-assembled single-atom nanozyme which allows oxygen generation to enhance PDT efficacy.

Catalase serves as a crucial component of the antioxidant defense system by catalyzing the decomposition of hydrogen peroxide into water and molecular oxygen. This study investigated the effects of 1 MeV accelerated electron irradiation on catalase activity in model solutions at doses of 100 Gy and 1000 Gy. Enzyme activity was assessed using two complementary methods: spectrophotometric analysis and the oxygen bubble method. The experimental results demonstrated dose-dependent inhibition of catalase activity, indicating that substantial radiation-induced structural modifications may occur in the enzyme molecule as a result of irradiation. To understand the relationship between the irradiation dose and the catalase inhibition, calibration curves plotting the dependencies of hydrogen peroxide decomposition rate and the delayed appearance of oxygen bubbles after adding hydrogen peroxide to catalase saline solution on the catalase concentration showed a 1.5-fold reduction in catalase activity at 100 Gy and a 40-fold decrease at 1000 Gy. Based on these findings, we propose a novel biodosimetry approach utilizing the oxygen bubble formation delay time as an express assessment tool for detecting high radiation doses absorbed by biological objects, for example, food products. The results obtained in the study have important implications for evaluating radiation effects on biological systems, in particular catalase-containing food products, offering potential applications in radiation safety monitoring and food quality control.

Although Prussian blue nanozymes (PBNZ) are widely applied in various fields, their catalytic mechanisms remain elusive. Here, we investigate the long-term catalytic performance of PBNZ as peroxidase (POD) and catalase (CAT) mimetics to elucidate their lifespan and underlying mechanisms. Unlike our previously reported Fe 3 O 4 nanozymes, which exhibit depletable POD-like activity, the POD and CAT-like activities of PBNZ not only persist but slightly enhance over prolonged catalysis. We demonstrate that the irreversible oxidation of PBNZ significantly promotes catalysis, leading to self-increasing catalytic activities. The catalytic process of the pre-oxidized PBNZ can be initiated through either the conduction band pathway or the valence band pathway. In summary, we reveal that PBNZ follows a dual-path electron transfer mechanism during the POD and CAT-like catalysis, offering the advantage of a long service life. Sustained catalytic performance wound benefit the applications of nanozymes, but the catalytic activity of some nanozymes depletes with time. Here the authors report Prussian blue nanozymes that exhibit self-increasing catalytic activity and elucidate the underlying catalytic mechanisms.

Free radicals, products of oxidative processes, induce cellular damage linked to diseases like Parkinson's and diabetes due to increased reactive oxygen species (ROS) levels. Catalase, crucial for scavenging ROS, emerges as a therapeutic agent against ailments including atherosclerosis and tumor progression. Its primary function involves breaking down hydrogen peroxide into water and oxygen. Research on catalase-drug interactions reveals structural changes under specific conditions, affecting its activity and cellular antioxidant balance, highlighting its pivotal role in defending against oxidative stress-related diseases. Hence, targeting catalase is considered an effective strategy for controlling ROS-induced cellular damage. This study investigates the interaction between bovine liver catalase and glipizide using spectroscopic and computational methods. It also explores glipizide's effect on catalase activity. More than 20% inhibition of catalase enzymatic activity was recorded in the presence of 50 µM glipizide. To investigate the inhibition of catalase activity by glipizide, we performed a series of binding studies. Glipizide was found to form a complex with catalase with moderate affinity and binding constant in the range of 3.822 to 5.063 × 10 4 M −1 . The binding was spontaneous and entropically favourable. The α-helical content of catalase increased from 24.04 to 29.53% upon glipizide complexation. Glipizide binding does not alter the local environment surrounding the tyrosine residues while a notable decrease in polarity around the tryptophan residues of catalase was recorded. Glipizide interacted with numerous active site residues of catalase including His361, Tyr357, Ala332, Asn147, Arg71, and Thr360. Molecular simulations revealed that the catalase-glipizide complex remained relatively stable in an aqueous environment. The binding of glipizide had a negligible effect on the secondary structure of catalase, and hydrogen bonds persisted consistently throughout the trajectory. These results could aid in the development of glipizide as a potent catalase inhibitor, potentially reducing the impact of reactive oxygen species (ROS) in the human body.

The optimization of the enzyme-like catalytic selectivity of nanozymes for specific reactive oxygen species (ROS)-related applications is significant, and meanwhile the real-time monitoring of ROS is really crucial for tracking the therapeutic process. Herein, we present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO 3-x nanozymes (denoted as MF-x, x: oxidation time) in a controlled manner aiming to improve their specificity of H 2 O 2 -associated catalytic reactions for specific therapy and monitoring of ROS-related diseases. Experimentally, MF-0 (Mo average valence 4.64) and MF-10 (Mo average valence 5.68) exhibit exclusively optimal catalase (CAT)- or peroxidase (POD)-like activity, respectively. Density functional theory (DFT) calculations verify the most favorable reaction path for both MF-0- and MF-10-catalyzed reaction processes based on free energy diagram and electronic structure analysis, disclosing the mechanism of the H 2 O 2 activation pathway on the Mo-based nanozymes. Furthermore, MF-0 poses a strong potential in acute kidney injury (AKI) treatment, achieving excellent therapeutic outcomes in vitro and in vivo. Notably, the ROS-responsive photoacoustic imaging (PAI) signal of MF-0 during treatment guarantees real-time monitoring of the therapeutic effect and post-cure assessment in vivo, providing a highly desirable non-invasive diagnostic approach for ROS-related diseases. Nanozymes can mimic the activity of natural enzymes but are limited by poor reaction selectivity due to the lack of enzyme-like molecular recognition units as in natural enzymes. Here, the authors present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO 3-x nanozymes and show they can exhibit exclusive catalase- or peroxidase-like activities.

More than ten ergot alkaloids comprising both natural and semi-synthetic products are used to treat various diseases 1 , 2 . The central C ring forms the core pharmacophore for ergot alkaloids, giving them structural similarity to neurotransmitters, thus enabling their modulation of neurotransmitter receptors 3 . The haem catalase chanoclavine synthase (EasC) catalyses the construction of this ring through complex radical oxidative cyclization 4 . Unlike canonical catalases, which catalyse H 2 O 2 disproportionation 5 , 6 , EasC and its homologues represent a broader class of catalases that catalyse O 2 -dependent radical reactions 4 , 7 . We have elucidated the structure of EasC by cryo-electron microscopy, revealing a nicotinamide adenine dinucleotide phosphate (reduced) (NADPH)-binding pocket and a haem pocket common to all haem catalases, with a unique homodimeric architecture that is, to our knowledge, previously unobserved. The substrate prechanoclavine unprecedentedly binds in the NADPH-binding pocket, instead of the previously suspected haem-binding pocket, and two pockets were connected by a slender tunnel. Contrary to the established mechanisms, EasC uses superoxide rather than the more generally used transient haem iron–oxygen complexes (such as compounds I, II and III) 8 , 9 , to mediate substrate transformation through superoxide-mediated cooperative catalysis of the two distant pockets. We propose that this reactive oxygen species mechanism could be widespread in metalloenzyme-catalysed reactions. The unique structure and mechanism of chanoclavine synthase (EasC), a haem catalase that uses superoxide for substrate transformation in ergot alkaloid biosynthesis, are revealed in this study, challenging established catalase mechanisms.

Downy mildew of pearl millet caused by the biotrophic oomycete Sclerospora graminicola is the most devastating disease which impairs pearl millet production causing huge yield and monetary losses. Chitosan nanoparticles (CNP) were synthesized from low molecular weight chitosan having higher degree of acetylation was evaluated for their efficacy against downy mildew disease of pearl millet caused by Sclerospora graminicola. Laboratory studies showed that CNP seed treatment significantly enhanced pearl millet seed germination percentage and seedling vigor compared to the control. Seed treatment with CNP induced systemic and durable resistance and showed significant downy mildew protection under greenhouse conditions in comparison to the untreated control. Seed treatment with CNP showed changes in gene expression profiles wherein expression of genes of phenylalanine ammonia lyase, peroxidase, polyphenoloxidase, catalase and superoxide dismutase were highly upregulated. CNP treatment resulted in earlier and higher expression of the pathogenesis related proteins PR1 and PR5. Downy mildew protective effect offered by CNP was found to be modulated by nitric oxide and treatment with CNP along with NO inhibitors cPTIO completely abolished the gene expression of defense enzymes and PR proteins. Further, comparative analysis of CNP with Chitosan revealed that the very small dosage of CNP performed at par with recommended dose of Chitosan for downy mildew management.