A novel fluorimetric method for laccase activities measurement using Amplex Red as substrate

Nernst-Michaelis-Menten framework unlocks electrochemical kinetics for laccases

Determining oxidoreductase kinetic parameters remains challenging due to spectrophotometric method limitations. Here, we present an innovative approach combining electrochemistry and enzymology principles through a novel Nernst-Michaelis-Menten theoretical framework. This model merges the Nernst equation, describing electrochemical equilibrium, with Michaelis-Menten kinetics, enabling accurate enzyme parameters determination, via chronopotentiometry. Using a commercial laccase from Trametes versicolor as a model system, we demonstrate precise kinetic parameters measurement for both chromophoric (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) - ABTS, Km = (56.7 ± 6.3) μM) and non-chromophoric (hydroquinone, Km = (196 ± 59) μM) substrates, validated against established techniques. The method requires minimal enzyme quantities and enables rapid analysis. This approach overcomes current methodological limitations and extends to other oxidoreductases, providing a powerful tool for enzyme characterization. Our work provides a new paradigm for enzyme kinetics, expanding the scope of analysable enzymatic systems, including those that were previously challenging to characterize with conventional methods.

Laccase Functional Analysis: Substrates, Activity Assays, Challenges, and Prospects

Enzyme functional analysis is a multifaceted process that can be used for various purposes, such as screening for specific activities, as well as developing, optimising, and validating processes or final products. Functional analysis methods are crucial for assessing enzyme performance and catalytic properties. Laccase, a well-known blue multi-copper oxidase, holds immense potential in diverse industries such as pharmaceuticals, paper and pulp, food and beverages, textiles, and biorefineries due to its clean oxidation process and versatility in handling a wide range of substrates. Despite its prominence, the use of laccase encounters challenges in selecting appropriate functional analysis substrates and methods. This review delves into the substrates utilised in qualitative and quantitative techniques for laccase activity analysis. Although laccase catalyses mono-electron oxidation of aromatic hydroxyl, amine, and thiol compounds efficiently, using molecular oxygen as an electron acceptor, the review identifies limitations in the specificity of the commonly employed substrates, concerns regarding the stability of certain compounds and highlights potential strategies.

A highly sensitive caffeic acid fluorescent probe for detecting laccase in grape juice and mushrooms

Laccase is a kind of copper-containing polyphenol oxidase obtained with similar properties from different sources, and its catalytic reaction requires only oxygen and releases only water. The most widely used method for laccase detection is spectrophotometric assay with limited sensitivity. Herein, we report a highly sensitive fluorescence method for detecting the activity of laccase. The reported probe shows high selectivity, reliable accuracy and a good linear relationship toward different concentrations of laccase. Upon reaction, a new absorption peak appears around 420 nm accompanied by a significant fluorescence increase at 470 nm, which was consistent with the conjugation extension after the polyphenol structure was oxidized to quinone. The effects of different inhibitors and metal ions on the activity of laccase were assessed and the probe was compared with a commercial laccase detection kit and it showed higher sensitivity. Furthermore, this method was successfully used for the determination of laccase in grape musts with different degrees of fermentation as well as in three kinds of mushroom extracts.

Recent advances in laccase activity assays: A crucial challenge for applications on complex substrates

Despite being one of the first enzymes discovered in 1883, the determination of laccase activity remains a scientific challenge, and a barrier to the full use of laccase as a biocatalyst. Indeed, laccase, an oxidase of the blue multi-copper oxidases family, has a wide range of substrates including substituted phenols, aromatic amines and lignin-related compounds. Its one-electron mechanism requires only oxygen and releases water as a reaction product. These characteristics make laccase a biocatalyst of interest in many fields of applications including pulp and paper industry, biorefineries, food, textile, and pharmaceutical industries. But to fully envisage the use of laccase at an industrial scale, its activity must be reliably quantifiable on complex substrates and in complex matrices. This review aims to describe current and emerging methods for laccase activity assays and place them in the context of a potential industrial use of the enzyme.

An Optical Sensing Platform for Beta-Glucosidase Activity Using Protein-Inorganic Hybrid Nanoflowers

In this work, a convenient and dual-signal readout optical sensing platform for the sensitively and selectively determination of beta-glucosidase (β-Glu) activity was reported using protein-inorganic hybrid nanoflowers [BSA-Cu₃(PO₄)₂·3H₂O] possessing peroxidase-mimicking activity. The nanoflowers (NFs) were facilely synthesized through a self-assembled synthesis strategy at room temperature. The as-prepared NFs could catalytically convert the colorless and non-fluorescent Amplex Red into colored and highly fluorescent resorufin in the presence of hydrogen peroxide via electron transfer process. β-Glu could hydrolyze cyanogenic glycoside, using amygdalin (Amy) as a model, into cyanide ions (CN^-), which can subsequently efficiently suppress the catalytic activity of NFs, accompanied with the fluorescence decrease and the color fading. The concentration of CN^- was controlled by β-Glu-triggered enzymatic reaction of Amy. Thus, a sensing system was established for fluorescent and visual determination of β-Glu activity. Under the optimum conditions, the present fluorescent and visual bimodal sensing platform exhibited good sensitivity for β-Glu activity assay with a detection limit of 0.33 U·L^-1. The sensing platform was further applied to determinate β-Glu in real samples and satisfactory results were attained. Additionally, the optical sensing system can potentially be a promising candidate for β-Glu inhibitors screening.

New Inhibitors of Laccase and Tyrosinase by Examination of Cross-Inhibition between Copper-Containing Enzymes

Coppers play crucial roles in the maintenance homeostasis in living species. Approximately 20 enzyme families of eukaryotes and prokaryotes are known to utilize copper atoms for catalytic activities. However, small-molecule inhibitors directly targeting catalytic centers are rare, except for those that act against tyrosinase and dopamine-β-hydroxylase (DBH). This study tested whether known tyrosinase inhibitors can inhibit the copper-containing enzymes, ceruloplasmin, DBH, and laccase. While most small molecules minimally reduced the activities of ceruloplasmin and DBH, aside from known inhibitors, 5 of 28 tested molecules significantly inhibited the function of laccase, with the K_i values in the range of 15 to 48 µM. Enzyme inhibitory kinetics classified the molecules as competitive inhibitors, whereas differential scanning fluorimetry and fluorescence quenching supported direct bindings. To the best of our knowledge, this is the first report on organic small-molecule inhibitors for laccase. Comparison of tyrosinase and DBH inhibitors using cheminformatics predicted that the presence of thione moiety would suffice to inhibit tyrosinase. Enzyme assays confirmed this prediction, leading to the discovery of two new dual tyrosinase and DBH inhibitors.

Oxidative polymerization process of hydroxytyrosol catalysed by polyphenol oxidases or peroxidase: Characterization, kinetics and thermodynamics

Hydroxytyrosol oligomer prepared by bioenzyme shows stronger health-promoting properties than its monomer. However, the polymerization process carried out by laccase, tyrosinase or horseradish peroxidase is still lacking in term of product characterization, kinetics and thermodynamics. To achieve these aspects, ATR-FT-IR, NMR, the Michaelis-Menten equation and isothermal titration calorimetry were explored. The results showed that the identified polymers presented a CC bond and a degree of polymerization less than six. Laccase showed the greatest affinity to hydroxytyrosol via comparison of K_m and V_m. All of these polymerization processes were spontaneous and exothermic behaviuors ranging from 30 to 50 °C, and were driven by hydrogen bonds, van der Waals interactions and hydrophobic interactions. Furthermore, circular dichroism spectroscopy was used to reveal the enzymatic structural changes during the catalysis, which showed that β-sheet levels for laccase, α-helix levels for tyrosinase, and the α-helix and random coil levels for horseradish peroxidase were dramatically decreased.

DNA-directed arrangement of soft synthetic compartments and their behavior in vitro and in vivo

DNA has been widely used as a key tether to promote self-organization of super-assemblies with emergent properties. However, control of this process is still challenging for compartment assemblies and to date the resulting assemblies have unstable membranes precluding in vitro and in vivo testing. Here we present our approach to overcome these limitations, by manipulating molecular factors such as compartment membrane composition and DNA surface density, thereby controlling the size and stability of the resulting DNA-linked compartment clusters. The soft, flexible character of the polymer membrane and low number of ssDNA remaining exposed after cluster formation determine the interaction of these clusters with the cell surface. These clusters exhibit in vivo stability and lack of toxicity in a zebrafish model. To display the breadth of therapeutic applications attainable with our system, we encapsulated the medically established enzyme laccase within the inner compartment and demonstrated its activity within the clustered compartments. Most importantly, these clusters can interact selectively with different cell lines, opening a new strategy to modify and expand cellular functions by attaching such pre-organized soft DNA-mediated compartment clusters on cell surfaces for cell engineering or therapeutic applications.

Fluorescence detection of laccases activity by the photoinduced electron transfer (PET) process

Laccases play a vital role in some physiological processes, for example in morphogenesis, carbon cycle, and defense against parasitism. So, designing a high-sensitivity accurate method is essential for researchers. In this study, a simple fluorescence method based on the function of carbon nitride (g-C₃N₄) by dopamine is synthesized. For the design of this sensor, carbon nitride (g-C₃N₄) is initially synthesis by using a simple method, which is carried out by heating melamine at 550 °C for 3 h and modifying it with dopamine by a linker such as glutaraldehyde. However, the g-C₃N₄-Dopa produced by this method, with an excitation wavelength of 330 nm, has a fluorescence emission at 466 nm. When laccase and g-C₃N₄-Dopa were mixed, dopamine with redox property was oxidized to dopaquinone; this causes the phenomenon of photoinduced electron transfer (PET) process between g-C₃N₄ and the dopaquinone. Hence, fluorescence quenching occurs due to this phenomenon. As a result of these discussions, a sensor for the laccase activity was designed based on the fluorescence quenching degree, supporting a linear range of 0.0-400.0 U L^-1 with the detection limit of 2.0 U L^-1. Using this sensor, the activity of the laccase enzyme in the human serum samples is measured. Dopamine-functionalized carbon nitride was prepared and utilized for the highly sensitive detection of laccases activity.

A Robust Longitudinal Co-culture of Obligate Anaerobic Gut Microbiome With Human Intestinal Epithelium in an Anoxic-Oxic Interface-on-a-Chip

The majority of human gut microbiome is comprised of obligate anaerobic bacteria that exert essential metabolic functions in the human colon. These anaerobic gut bacteria constantly crosstalk with the colonic epithelium in a mucosal anoxic-oxic interface (AOI). However, in vitro recreation of the metabolically mismatched colonic AOI has been technically challenging. Furthermore, stable co-culture of the obligate anaerobic commensal microbiome and epithelial cells in a mechanically dynamic condition is essential for demonstrating the host-gut microbiome crosstalk. Here, we developed an anoxic-oxic interface-on-a-chip (AOI Chip) by leveraging a modified human gut-on-a-chip to demonstrate a controlled oxygen gradient in the lumen-capillary transepithelial interface by flowing anoxic and oxic culture medium at various physiological milieus. Computational simulation and experimental results revealed that the presence of the epithelial cell layer and the flow-dependent conditioning in the lumen microchannel is necessary and sufficient to create the steady-state vertical oxygen gradient in the AOI Chip. We confirmed that the created AOI does not compromise the viability, barrier function, mucin production, and the expression and localization of tight junction proteins in the 3D intestinal epithelial layer. Two obligate anaerobic commensal gut microbiome, Bifidobacterium adolescentis and Eubacterium hallii, that exert metabolic cross-feeding in vivo, were independently co-cultured with epithelial cells in the AOI Chip for up to a week without compromising any cell viability. Our new protocol for creating an AOI in a microfluidic gut-on-a-chip may enable to demonstrate the key physiological interactions of obligate anaerobic gut microbiome with the host cells associated with intestinal metabolism, homeostasis, and immune regulation.

A far-red fluorescent probe for sensing laccase in fungi and its application in developing an effective biocatalyst for the biosynthesis of antituberculous dicoumarin

A far-red fluorescent probe for sensing laccase in fungi and its application in developing an effective biocatalyst for the biosynthesis of antituberculous dicoumarin.