Conformational flexibility related to enzyme activity: evidence for a dynamic active-site gatekeeper function of Tyr(215) in Aerococcus viridans lactate oxidase

C-terminal lysine residues enhance plasminogen activation by inducing conformational flexibility and stabilization of activator complex of staphylokinase with plasmin

Staphylokinase (SAK), a potent fibrin-specific plasminogen activator secreted by Staphylococcus aureus, carries a pair of lysine at the carboxy-terminus that play a key role in plasminogen activation. The underlaying mechanism by which C-terminal lysins of SAK modulate its function remains unknown. This study has been undertaken to unravel role of C-terminal lysins of SAK in plasminogen activation. While deletion of C-terminal lysins (Lys135, Lys136) drastically impaired plasminogen activation by SAK, addition of lysins enhanced its catalytic activity 2-2.5-fold. Circular dichroism analysis revealed that C-terminally modified mutants of SAK carry significant changes in their beta sheets and secondary structure. Structure models and RING (residue interaction network generation) studies indicated that the deletion of lysins has conferred extensive topological alterations in SAK, disrupting vital interactions at the interface of SAK.plasmin complex, thereby leading significant impairment in its functional activity. In contrast, addition of lysins at the C-terminus enhanced its conformational flexibility, creating a stronger coupling at the interface of SAK.plasmin complex and making it more efficient for plasminogen activation. Taken together, these studies provided new insights on the role of C-terminal lysins in establishment of precise intermolecular interactions of SAK with the plasmin for the optimal function of activator complex.

Nitrogen-Centered Lactate Oxidase Nanozyme for Tumor Lactate Modulation and Microenvironment Remodeling

Designing nanozymes that match natural enzymes have always been an attractive and challenging goal. In general, researchers mainly focus on the construction of metal centers and the control of non-metallic ligands of nanozyme to regulate their activities. However, this is not applicable to lactate oxidase, i.e., flavoenzymes with flavin mononucleotide (FMN)-dependent pathways. Herein, we propose a coordination strategy to mimic lactate oxidase based on engineering the electronic properties at the N center by modulating the Co number near N in the Co_x-N nanocomposite. Benefitting from the manipulated coordination fields and electronic structure around the electron-rich N sites, Co₄N/C possesses a precise recognition site for lactate and intermediate organization and optimizes the absorption energies for intermediates, leading to superior oxidation of the lactate α-C-sp(3)-H bond toward ketone. The optimized nanozyme delivers much improved anticancer efficacy by reversing the high lactate and the immunosuppressive state of the tumor microenvironment, subsequently achieving excellent tumor growth and distant metastasis inhibition. The developed Co₄N/C NEs open a new window for building a bridge between chemical catalysis and biocatalysis.

His-tagged lactate oxidase production for industrial applications using fed-batch fermentation

L-lactate oxidase (LOX) is a biotechnologically important enzyme used in biosensors and colorimetric kits to detect lactate, a key biomarker in clinical diagnostics, sports medicine and the food industry. In this work, we produced a recombinant His-tagged Aerococcus viridans LOX (rLOX) in Escherichia coli and carried out its functional characterization for industrial applications. Our rLOX was evaluated in a colorimetric kit for human diagnostics and in an amperometric biosensor to measure the lactic acid in food products. The rLOX was fully functional for both applications, with a performance comparable to commercial untagged LOXs. As the industrial use of LOX enzyme requires a large-scale production, we scaled up the rLOX production in a fed-batch bioreactor culture and obtained a yield approximately ten times higher than that of the Erlenmeyer scale. The His-tag allowed an easy and highly efficient purification process, and a high-purity rLOX was recovered after this one-step affinity purification. In this study, we described a simple, rapid and cost-competitive approach for the production of a recombinant His-tagged LOX enzyme suitable for industrial use.

Activation of L-lactate oxidase by the formation of enzyme assemblies through liquid-liquid phase separation

The assembly state of enzymes is gaining interest as a mechanism for regulating the function of enzymes in living cells. One of the current topics in enzymology is the relationship between enzyme activity and the assembly state due to liquid-liquid phase separation. In this study, we demonstrated enzyme activation via the formation of enzyme assemblies using L-lactate oxidase (LOX). LOX formed hundreds of nanometer-scale assemblies with poly-L-lysine (PLL). In the presence of ammonium sulfate, the LOX-PLL clusters formed micrometer-scale liquid droplets. The enzyme activities of LOX in clusters and droplets were one order of magnitude higher than those in the dispersed state, owing to a decrease in K_M and an increase in k_cat. Moreover, the clusters exhibited a higher activation effect than the droplets. In addition, the conformation of LOX changed in the clusters, resulting in increased enzyme activation. Understanding enzyme activation and assembly states provides important information regarding enzyme function in living cells, in addition to biotechnology applications.

MDexciteR: Enhanced Sampling Molecular Dynamics by Excited Normal Modes or Principal Components Obtained from Experiments

Molecular dynamics with excited normal modes (MDeNM) is an enhanced sampling method for exploring conformational changes in proteins with minimal biases. The excitation corresponds to injecting kinetic energy along normal modes describing intrinsic collective motions. Herein, we developed a new automated open-source implementation, MDexciteR (https://github.com/mcosta27/MDexciteR), enabling the integration of MDeNM with two commonly used simulation programs with GPU support. Second, we generalized the method to include the excitation of principal components calculated from experimental ensembles. Finally, we evaluated whether the use of coarse-grained normal modes calculated with elastic network representations preserved the performance and accuracy of the method. The advantages and limitations of these new approaches are discussed based on results obtained for three different protein test cases: two globular and a protein/membrane system.

Flavin Mononucleotide-Dependent l-Lactate Dehydrogenases: Expanding the Toolbox of Enzymes for l-Lactate Biosensors

The development of L-lactate biosensors has been hampered in recent years by the lack of availability and knowledge about a wider range and diversity of L-lactate-oxidizing enzymes that can be used as bioelements in these sensors. For decades, L-lactate oxidase of Aerococcus viridans (AvLOx) has been used almost exclusively in the field of L-lactate biosensor development and has achieved somewhat like a monopoly status as a biocatalyst for these applications. Studies on other L-lactate-oxidizing enzymes are sparse and are often missing biochemical data. In this work, we made use of the vast amount of sequence information that is currently available on protein databases to investigate the naturally occurring diversity of L-lactate-utilizing enzymes of the flavin mononucleotide (FMN)-dependent α-hydroxy acid oxidoreductase (HAOx) family. We identified the HAOx sequence space specific for L-lactate oxidation and additionally discovered a not-yet described class of soluble and FMN-dependent L-lactate dehydrogenases, which are promising for the construction of second-generation biosensors or other biotechnological applications. Our work paves the way for new studies on α-hydroxy acid biosensors and proves that there is more to the HAOx family than AvLOx.

Structure of lactate oxidase from Enterococcus hirae revealed new aspects of active site loop function: Product-inhibition mechanism and oxygen gatekeeper

l-Lactate oxidase (LOx) is a flavin mononucleotide (FMN)-dependent triose phosphate isomerase (TIM) barrel fold enzyme that catalyzes the oxidation of l-lactate using oxygen as a primary electron acceptor. Although reductive half-reaction mechanism of LOx has been studied by structure-based kinetic studies, oxidative half-reaction and substrate/product-inhibition mechanisms were yet to be elucidated. In this study, the structure and enzymatic properties of wild-type and mutant LOxs from Enterococcus hirae (EhLOx) were investigated. EhLOx structure showed the common TIM-barrel fold with flexible loop region. Noteworthy observations were that the EhLOx crystal structures prepared by co-crystallization with product, pyruvate, revealed the complex structures with "d-lactate form ligand," which was covalently bonded with a Tyr211 side chain. This observation provided direct evidence to suggest the product-inhibition mode of EhLOx. Moreover, this structure also revealed a flip motion of Met207 side chain, which is located on the flexible loop region as well as Tyr211. Through a saturation mutagenesis study of Met207, one of the mutants Met207Leu showed the drastically decreased oxidase activity but maintained dye-mediated dehydrogenase activity. The structure analysis of EhLOx Met207Leu revealed the absence of flipping in the vicinity of FMN, unlike the wild-type Met207 side chain. Together with the simulation of the oxygen-accessible channel prediction, Met207 may play as an oxygen gatekeeper residue, which contributes oxygen uptake from external enzyme to FMN. Three clades of LOxs are proposed based on the difference of the Met207 position and they have different oxygen migration pathway from external enzyme to active center FMN.

Dual activities of oxidation and oxidative decarboxylation by flavoenzymes

Specific flavoenzyme oxidases catalyze oxidative decarboxylation in addition to their classical oxidation reactions in the same active sites. The mechanisms underlying oxidative decarboxylation by these enzymes and how they control their two activities are not clearly known. This article reviews the current state of knowledge of four enzymes from the l-amino acid oxidase and l-hydroxy acid oxidase families, including l-tryptophan 2-monooxygenase, l-phenylalanine 2-oxidase and l-lysine oxidase/monooxygenase and lactate monooxygenase which catalyze substrate oxidation and oxidative decarboxylation. Apart from specific interactions to allow substrate oxidation by the flavin cofactor, specific binding of oxidized product in the active sites appears to be important for enabling subsequent decarboxylation by these enzymes. Based on recent findings of l-lysine oxidase/monooxygenase, we propose that nucleophilic attack of H2O2 on the imino acid product is the mechanism enabling oxidative decarboxylation.

Design and development of ferrocene-containing chitosan-cografted-branched polyethylenimine redox conjugates for monitoring free flap failure after reconstructive surgery

We reported a proof-of-concept study of developing an electrochemical biosensor for prolonged continuous monitoring free flap failure caused by vascular occlusion after reconstructive surgery. Ferrocene (Fc)-containing Chitosan-cografted-Branched Polyethylenimine redox conjugates (CHIT-Fc-co-BPEI-Fc) were used as pH-tuneable matrix to attach the target enzymes (glucose oxidase ≡ GOD and lactate oxidase ≡ LOD, respectively) to build up the corresponding GOD-sensor and LOD-sensor. The sensitivity of GOD-/LOD-sensor was found to be 2.89(±0.06)μA/mM and 2.95(±0.19)μA/mM with a limit of detection (LOD) of 0.047 mM and 0.172 mM, respectively. The sensor performance was further pre-clinically validated via rabbit study, which confirmed that the designed biosensors could electrochemically detect the changes of metabolite levels caused by flap failure within minutes. This sensor protocol is able to be fabricated as embedded biosensor for prolong continuous detection for clinical application/research.

TiO2 Nanotubes Alginate Hydrogel Scaffold for Rapid Sensing of Sweat Biomarkers: Lactate and Glucose

Versatile sensing matrixes are essential for the development of enzyme-immobilized optical biosensors. A novel three-dimensional titanium dioxide nanotubes/alginate hydrogel scaffold is proposed for the detection of sweat biomarkers, lactate, and glucose in artificial sweat. Hydrothermally synthesized titanium dioxide nanotubes were introduced to the alginate polymeric matrix, followed by cross-linking nanocomposite with dicationic calcium ions to fabricate the scaffold platform. Rapid colorimetric detection (blue color optical signal) was carried out for both lactate and glucose biomarkers in artificial sweat at 4 and 6 min, respectively. The superhydrophilicity and the capillarity of the synthesized titanium dioxide nanotubes, when incorporated into the alginate matrix, facilitate the rapid transfer of the artificial sweat components throughout the sensor scaffold, decreasing the detection times. Moreover, the scaffold was integrated on a cellulose paper to demonstrate the adaptability of the material to other matrixes, obtaining fast and homogeneous colorimetric detection of lactate and glucose in the paper substrate when image analysis was performed. The properties of this new composite provide new avenues in the development of paper-based sensor devices. The biocompatibility, the efficient immobilization of biological enzymes/colorimetric assays, and the quick optical signal readout behavior of the titanium dioxide nanotubes/alginate hydrogel scaffolds provide a prospective opportunity for integration into wearable devices.

Reducing l-lactate release from hippocampal astrocytes by intracellular oxidation increases novelty induced activity in mice

Astrocytes are in control of metabolic homeostasis in the brain and support and modulate neuronal function in various ways. Astrocyte-derived l-lactate (lactate) is thought to play a dual role as a metabolic and a signaling molecule in inter-cellular communication. The biological significance of lactate release from astrocytes is poorly understood, largely because the tools to manipulate lactate levels in vivo are limited. We therefore developed new viral vectors for astrocyte-specific expression of a mammalianized version of lactate oxidase (LOx) from Aerococcus viridans. LOx expression in astrocytes in vitro reduced their intracellular lactate levels as well as the release of lactate to the extracellular space. Selective expression of LOx in astrocytes of the dorsal hippocampus in mice resulted in increased locomotor activity in response to novel stimuli. Our findings suggest that a localized decreased intracellular lactate pool in hippocampal astrocytes could contribute to greater responsiveness to environmental novelty. We expect that use of this molecular tool to chronically limit astrocytic lactate release will significantly facilitate future studies into the roles and mechanisms of intercellular lactate communication in the brain.

Flavoprotein monooxygenases: Versatile biocatalysts

Flavoprotein monooxygenases (FPMOs) are single- or two-component enzymes that catalyze a diverse set of chemo-, regio- and enantioselective oxyfunctionalization reactions. In this review, we describe how FPMOs have evolved from model enzymes in mechanistic flavoprotein research to biotechnologically relevant catalysts that can be applied for the sustainable production of valuable chemicals. After a historical account of the development of the FPMO field, we explain the FPMO classification system, which is primarily based on protein structural properties and electron donor specificities. We then summarize the most appealing reactions catalyzed by each group with a focus on the different types of oxygenation chemistries. Wherever relevant, we report engineering strategies that have been used to improve the robustness and applicability of FPMOs.

Interfacial behavior of Lactate Oxidase at Air-Subphase interface

This article investigates the main aspects of the surface chemistry properties of the lactate oxidase (LacOx) enzyme monolayer at the air-subphase interface. Surface chemistry study determined the important properties like the surface packing and stability of the formed layer, whereas the spectroscopic experiments provided information regarding its secondary structure conformation of the enzyme. We have demonstrated that the LacOx in the monolayer form remained active for extended time period. In accordance to the data obtained from the isotherm it was also found that LacOx forms a stable monolayer that does not aggregate at the air-subphase interface. The stability of the monolayer at the air-subphase interface was studied by using compression-decompression cycles which revealed the stability with no significant evidence of aggregates or irreversible domains. This was further confirmed by UV-vis absorption and fluorescence measurements. Spectra from circular dichroism (CD) showed that the LB film retains the characteristic of an α-helix conformation.

Effect of active-site aromatic residues Tyr or Phe on activity and stability of glucose 6-phosphate dehydrogenase from psychrophilic Arctic bacterium Sphingomonas sp

Cold-adapted enzymes maintain correct conformation at their active sites despite their intrinsically flexible structures. The psychrophilic Arctic bacterium Sphingomonas sp. PAMC 26621 has two glucose 6-phosphate dehydrogenase (G6PD) isozymes, SpG6PD1 involved in the Entner-Doudoroff pathway and SpG6PD2 in the oxidative pentose phosphate pathway. Structural modeling of SpG6PD1 showed that the hydroxyl group of Tyr¹⁷⁷ participates in substrate binding by forming a hydrogen bond with the phosphate group of glucose 6-phosphate, whereas in SpG6PD2, a Phe residue is present in the corresponding position of Tyr¹⁷⁷. In this study, we investigated how subtle differences in aromatic residues in the substrate-binding pocket of SpG6PD1 affect enzymatic activity and stability. Mutations of Tyr¹⁷⁷ to Ala, His, Phe, and Trp caused increases in the rigidity of the SpG6PD1 structure. Particularly, mutants Y177F and Y177W showed increased thermal stabilities compared to wild-type (WT) but 3- and 15-fold lower catalytic efficiencies, respectively. However, mutants Y177A and Y177H became heat-labile at moderate temperatures. These results indicate that an aromatic residue (Tyr or Phe) is necessary for the substrate-binding pocket of SpG6PD1; Tyr with its hydroxyl group is preferred for enzymatic activity, whereas the more hydrophobic Phe is preferred for thermal stability. Substitutions of bulky Trp for Tyr or Phe at this position resulted in substantial loss of activity. Our study suggests that delicate adjustment of aromatic residues can regulate the activity and stability of psychrophilic G6PD isozymes involved in different metabolic pathways.

FMN-dependent oligomerization of putative lactate oxidase from Pediococcus acidilactici

Lactate oxidases belong to a group of FMN-dependent enzymes and they catalyze a conversion of lactate to pyruvate with a release of hydrogen peroxide. Hydrogen peroxide is also utilized as a read out in biosensors to quantitate lactate levels in biological samples. Aerococcus viridans lactate oxidase is the best characterized lactate oxidase and our knowledge of lactate oxidases relies largely to studies conducted with that particular enzyme. Pediococcus acidilactici lactate oxidase is also commercially available for e.g. lactate measurements, but this enzyme has not been characterized in detail before. Here we report structural characterization of the recombinant enzyme and its co-factor dependent oligomerization. The crystal structures revealed two distinct conformations in the loop closing the active site, consistent with previous biochemical studies implicating the role of loop in catalysis. Despite the structural conservation of active site residues, we were not able to detect either oxidase or monooxygenase activity when L-lactate was used as a substrate. Pediococcus acidilactici lactate oxidase is therefore an example of a misannotation of an FMN-dependent enzyme, which catalyzes likely a so far unknown oxidation reaction.

Rational engineering of Aerococcus viridansl-lactate oxidase for the mediator modification to achieve quasi-direct electron transfer type lactate sensor

The l-lactate oxidase (LOx) based lactate sensors are widely used for clinical diagnostics, sports medicine, and food quality control. However, dissolved oxygen interference and electroactive interferent effects are inherent issues of current lactate sensors. In this paper, a quasi-direct electron transfer (quasi-DET) type lactate sensor was developed using rationally engineered Aerococcus viridans LOx (AvLOx) modified with amine-reactive phenazine ethosulfate (PES). Since the modification of wild type AvLOx by PES did not result quasi-DET, engineered AvLOx with additional Lys residue was designed. The additional Lys residue was introduced by substituting residue locating on the surface of AvLOx, and within 20 Å of the isoalloxazine ring of FMN. Among several constructed mutants, Ala96Leu/Asn212Lys double mutant showed the highest dye-mediated dehydrogenase activity with negligible oxidase activity, showing quasi-DET properties after PES modification, when the enzyme was immobilized on screen printed carbon electrode. The constructed electrode did not show oxygen interference in cyclic voltammetric analysis and distinct catalytic current with 20 mM l-lactate. The sensor performance of a chronoamperometric l-lactate sensor employing PES modified Ala96Leu/Asn212Lys AvLOx, marked with linear range between 0 and 1 mM, with sensitivity of 13 μA/mM∙cm², and a limit of detection of 25 μM for l-lactate. By applying -200 mV vs. Ag/AgCl, l-lactate could be monitored with negligible interference from 170 μM ascorbic acid, 1.3 mM acetaminophen, 1.4 mM uric acid or 20 mM glucose. These results indicated that a quasi-DET type lactate sensor was developed that did not suffer from the interference of oxygen and representative electroactive ingredient compounds.

In Silico insights on enhancing thermostability and activity of a plant Fructosyltransferase from Pachysandra terminalis via introduction of disulfide bridges

Drawbacks of industrially-used fructosyltransferases (FTs) such as low optimum temperature and low fructooligosaccharides (FOS) yield necessitates the search for engineered FTs that are highly thermostable and active. With the availability of the first plant FT crystal structure from Pachysandra terminalis (PDB ID: 3UGH), computer-aided protein engineering of plant FT is now feasible. To obtain insights on the effect of specific mutations i.e. disulfide bridge introduction, wild-type and mutant FTs were subjected to a 15 μs Martini Coarse-grained Molecular Dynamics (CGMD) simulations at 303 K and 334 K. We report here the five mutants, M31C-Q49C, L144C-S193C, P34C-W300C, S219C-L226C and V470C-S498C with enhanced thermostabilities and/or activities relative to the wild type. Interestingly, M31C-Q49C, which is located within the catalytic-carrying blade of the catalytic domain, has an activity enhancement at both temperatures. At 334 K, three mutations, L144C-S193C, P34C-W300C and V470C-S498C, achieved thermostability relative to the wild type. Intriguingly, both activity and stability enhancement exhibited only at 334 K can be achieved provided that the mutation is located either on the catalytic-carrying residue blade of the catalytic domain or on the non-catalytic domain. Our results suggest that V470C-S498C and L144C-S193C are promising mutants and that domain-specific approach may be exploited to customize enzyme properties.

Structure and role for active site lid of lactate monooxygenase from Mycobacterium smegmatis

Lactate monooxygenase (LMO) catalyzes the FMN-dependent "coupled" oxidation of lactate and O₂ to acetate, carbon dioxide, and water, involving pyruvate and hydrogen peroxide as enzyme-bound intermediates. Other α-hydroxy acid oxidase family members follow an "uncoupled pathway," wherein the α-keto acid product quickly dissociates before the reduced flavin reacts with oxygen. Here, we report the structures of Mycobacterium smegmatis wild-type LMO and a wild-type-like C203A variant at 2.1 Å and 1.7 Å resolution, respectively. The overall LMO fold and active site organization, including a bound sulfate mimicking substrate, resemble those of other α-hydroxy acid oxidases. Based on structural similarity, LMO is similarly distant from lactate oxidase, glycolate oxidase, mandelate dehydrogenase, and flavocytochrome b₂ and is the first representative enzyme of its type. Comparisons with other α-hydroxy acid oxidases reveal that LMO has a longer and more compact folded active site loop (Loop 4), which is known in related flavoenzymes to undergo order/disorder transitions to allow substrate/product binding and release. We propose that LMO's Loop 4 has an enhanced stability that is responsible for the slow product release requisite for the coupled pathway. We also note electrostatic features of the LMO active site that promote substrate binding. Whereas the physiological role of LMO remains unknown, we document what can currently be assessed of LMO's distribution in nature, including its unexpected occurrence, presumably through horizontal gene transfer, in halophilic archaea and in a limited group of fungi of the genus Beauveria. BROAD STATEMENT OF IMPACT: This first crystal structure of the FMN-dependent α-hydroxy acid oxidase family member lactate monooxygenase (LMO) reveals it has a uniquely large active site lid that we hypothesize is stable enough to explain the slow dissociation of pyruvate that leads to its "coupled" oxidation of lactate and O₂ to produce acetate, carbon dioxide, and water. Also, the relatively widespread distribution of putative LMOs supports their importance and provides new motivation for their further study.

Computational engineering of cellulase Cel9A-68 functional motions through mutations in its linker region

Cellulase collective motions design through linker mutations leads to the enhancement of protein flexibility and function.

Roles of Active-Site Aromatic Residues in Cold Adaptation of Sphingomonas glacialis Esterase EstSP1

The aromatic amino acids, Tyr or Trp, which line the active-site walls of esterases, stabilize the catalytic His loop via hydrogen bonding. A Tyr residue is preferred in extremophilic esterases (psychrophilic or hyperthermophilic esterases), whereas a Trp residue is preferred in moderate-temperature esterases. Here, we provide evidence that Tyr and Trp play distinct roles in cold adaptation of the psychrophilic esterase EstSP1 isolated from an Arctic bacterium Sphingomonas glacialis PAMC 26605. Stern-Volmer plots showed that the mutation of Tyr191 to Ala, Phe, Trp, and His resulted in reduced conformational flexibility of the overall protein structure. Interestingly, the Y191W and Y191H mutants showed increased thermal stability at moderate temperatures. All Tyr191 mutants showed reduced catalytic activity relative to wild-type EstSP1. Our results indicate that Tyr with its phenyl hydroxyl group is favored for increased conformational flexibility and high catalytic activity of EstSP1 at low temperatures at the expense of thermal stability. The results of this study suggest that, in the permanently cold Arctic zone, enzyme activity has been selected for psychrophilic enzymes over thermal stability. The results presented herein provide novel insight into the roles of Tyr and Trp residues for temperature adaptation of enzymes that function at low, moderate, and high temperatures.

Upconversion Nanocarriers Encapsulated with Photoactivatable Ru Complexes for Near-Infrared Light-Regulated Enzyme Activity

Enzyme activity is important for metabolism, cell functions, and treating diseases. However, remote control of enzyme activity in deep tissue remains a challenge. This study demonstrates near-infrared (NIR) light-regulated enzyme activity in living cells based on upconverting nanoparticles (UCNPs) and a photoactivatable Ru complex. The Ru complex is a caged enzyme inhibitor that can be activated by blue light. To prepare a nanocarrier for NIR photoinhibition of enzyme activity, a UCNP and the caged enzyme inhibitors are encapsulated in a hollow mesoporous silica nanoparticle. In such a nanocarrier, the UCNP can harvest NIR light and convert it into blue light, which can activate the caged enzyme inhibitors. This photoactivation process is feasible in deep tissue because of the tissue penetration ability of NIR light. The nanocarrier is compatible to LNCaP, PC3, and SAOS-2 cells, which show high enzyme expression. NIR irradiation induces release of the inhibitors and inhibition of enzyme activity in living cells. NIR light provides high spatiotemporal resolution to regulate enzyme activity in deep tissue.

Amine oxidation by d-arginine dehydrogenase in Pseudomonas aeruginosa

d-Arginine dehydrogenase from Pseudomonas aeruginosa (PaDADH) is a flavin-dependent oxidoreductase, which is part of a novel two-enzyme racemization system that functions to convert d-arginine to l-arginine. PaDADH contains a noncovalently linked FAD that shows the highest activity with d-arginine. The enzyme exhibits broad substrate specificity towards d-amino acids, particularly with cationic and hydrophobic d-amino acids. Biochemical studies have established the structure and the mechanistic properties of the enzyme. The enzyme is a true dehydrogenase because it displays no reactivity towards molecular oxygen. As established through solvent and multiple kinetic isotope studies, PaDADH catalyzes an asynchronous CH and NH bond cleavage via a hydride transfer mechanism. Steady-state kinetic studies with d-arginine and d-histidine are consistent with the enzyme following a ping-pong bi-bi mechanism. As shown by a combination of crystallography, kinetic and computational data, the shape and flexibility of loop L1 in the active site of PaDADH are important for substrate capture and broad substrate specificity.