Optical enzyme sensor for determining l-lysine content using l-lysine oxidase from the rockfish Sebastes schlegeli

A comprehensive review of methods for determination of l-lysine with detailed description of biosensors

l-lysine being one of the essential amino acids is not produced by the body, but is obtained through diet. l-lysine determination is important in the food and pharmaceutical industries as well as have medical and diagnostic applications. The normal l-lysine levels in a healthy human serum sample is 150 to 250 μmol/l. There is imbalance in l-lysine levels in certain diseased conditions. So, it could be a biomarker for diagnosis. Various basic methods are available for the determination of l-lysine such as colorimetric, radioisotope dilution, chromatographic, fluorometric and voltammetric methods. These methods have certain disadvantages like sample pretreatment, costly, time consuming and requirement of skilled personnel. These drawbacks are overcome by the use of biosensors due to their high sensitivity, stability and specificity. The present review article discusses about the principles, merits and demerits of the various analytic methods for determination of l-lysine with special emphasis on biosensors. l-lysine biosensors work ideally under the optimum pH 5 to 10, potential range -0.05 to 1.5 V, temperature 25 to 40 °C, with linear range 0.01 to 5500 μM, detection limit 0.000004 to 650 μM and response time 2 to 300 s. The sensor had storage stability between 14 and 200 days.

l-Amino acid oxidase as a fish host-defense molecule

An l-amino acid oxidase (LAO) is an amino acid metabolism enzyme that also performs a variety of biological activities. Recently, LAOs have been discovered to be deeply involved in innate immunity in fish because of their antibacterial and antiparasitic activity. The determinant of potent antibacterial/antiparasitic activity is the H₂O₂ byproduct of LAO enzymatic activity that utilizes the l-amino acid as a substrate. In addition, fish LAOs are upregulated by pathogenic bacteria or parasite infection. Furthermore, some fish LAOs show that the target specificity depends on the virulence of the bacteria. All results reflect that LAOs are new innate immune molecules. This review also describes the potential of the immunomodulatory functions of fish LAOs, not only the innate immune function by a direct oxidation attack of H₂O₂.

Distribution in Different Organisms of Amino Acid Oxidases with FAD or a Quinone As Cofactor and Their Role as Antimicrobial Proteins in Marine Bacteria

Amino acid oxidases (AAOs) catalyze the oxidative deamination of amino acids releasing ammonium and hydrogen peroxide. Several kinds of these enzymes have been reported. Depending on the amino acid isomer used as a substrate, it is possible to differentiate between l-amino acid oxidases and d-amino acid oxidases. Both use FAD as cofactor and oxidize the amino acid in the alpha position releasing the corresponding keto acid. Recently, a novel class of AAOs has been described that does not contain FAD as cofactor, but a quinone generated by post-translational modification of residues in the same protein. These proteins are named as LodA-like proteins, after the first member of this group described, LodA, a lysine epsilon oxidase synthesized by the marine bacterium Marinomonas mediterranea. In this review, a phylogenetic analysis of all the enzymes described with AAO activity has been performed. It is shown that it is possible to recognize different groups of these enzymes and those containing the quinone cofactor are clearly differentiated. In marine bacteria, particularly in the genus Pseudoalteromonas, most of the proteins described as antimicrobial because of their capacity to generate hydrogen peroxide belong to the group of LodA-like proteins.

Advances in non-snake venom L-amino acid oxidase

L-amino acid oxidase is widely found in diverse organisms and has different properties. It is thought to contribute to antimicrobial activity, amino acid catabolism, and so forth. The purpose of this communication is to summarize the advances in non-snake venom L-amino acid oxidase, including its enzymatic and structural properties, gene cloning and expression, and biological function. In addition, the mechanism of its biological function as well as its application is also discussed.

Fiber optic monooxygenase biosensor for toluene concentration measurement in aqueous samples

Measurements of pollutants such as toluene are critical for the characterization of contaminated sites and for the monitoring of remediation processes and wastewater treatment effluents. Fiber optic enzymatic biosensors have the potential to provide cost-effective, real time, continuous, in situ measurements. In this study, a fiber optic enzymatic biosensor was constructed and characterized for the measurement of toluene concentrations in aqueous solutions. The biological recognition element was toluene ortho-monooxygenase (TOM), expressed by Escherichia coli TG1 carrying pBS(Kan)TOM, while an optical fiber coated with an oxygen-sensitive ruthenium-based phosphorescent dye served as the transducer. Toluene was detected based on the enzymatic reaction catalyzed by TOM, which resulted in the consumption of oxygen and changes in the phosphorescence intensity. The biosensor was found to have a limit of detection of 3 μM, a linear signal range up to 100 μM, and a response time of 1 h. The performance was reproducible with different biosensors (RSD=7.4%, n=8). The biosensor activity declined with each measurement and with storage time, particularly at elevated temperatures. This activity loss could be partially reversed by exposure to formate, suggesting that NADH consumption was the primary factor limiting lifetime. This is the first report of an enzymatic toluene sensor and of an oxygenase-based biosensor. Since many oxygenases have been reported, the design concept of this oxygenase-based biosensor has the potential to broaden biosensor applications in environmental monitoring.

Discovery of serum L-amino acid oxidase in the rockfish Sebastes schlegeli: isolation and biochemical characterization

Fish have a complex innate defense mechanism against microbial invasion. In particular, epidermal mucus and serum in fish play important roles in innate immunity and contain a variety of bioactive substances such as complements, lectins and lysozymes, involved in host defense. Recently, L-amino acid oxidases (LAOs) with antibacterial activity were isolated from the skin and/or gill mucous secretions of rockfish, great sculpin and flounder, and were identified to be a novel type of antibacterial protein in the integument of fish. In the present study, we found LAO activity in the serum of rockfish Sebastes schlegeli. The LAO was isolated from the serum by sequential column chromatography of Con-A lectin affinity chromatography, anion exchange HPLC, hydroxyapatite HPLC and gel filtration HPLC, and characterized. The LAO (a molecular mass of 160 kDa) comprised subunits with a molecular mass of 53 kDa and showed strict substrate specificity, catalyzing only L-lysine with Km 0.37 mM and kcat 57.1s(-1). The serum LAO exhibited a broad antibacterial activity against Gram positive and negative bacteria, most potently against Aeromonas hydrophila and Aeromonas salmonicida with a minimum inhibitory concentration of 0.078 μg/mL. This is the first report of LAO in the serum of fish and its involvement in innate immunity in the rockfish body.

Finding new enzymes from bacterial physiology: a successful approach illustrated by the detection of novel oxidases in Marinomonas mediterranea

The identification and study of marine microorganisms with unique physiological traits can be a very powerful tool discovering novel enzymes of possible biotechnological interest. This approach can complement the enormous amount of data concerning gene diversity in marine environments offered by metagenomic analysis, and can help to place the activities associated with those sequences in the context of microbial cellular metabolism and physiology. Accordingly, the detection and isolation of microorganisms that may be a good source of enzymes is of great importance. Marinomonas mediterranea, for example, has proven to be one such useful microorganism. This Gram-negative marine bacterium was first selected because of the unusually high amounts of melanins synthesized in media containing the amino acid L-tyrosine. The study of its molecular biology has allowed the cloning of several genes encoding oxidases of biotechnological interest, particularly in white and red biotechnology. Characterization of the operon encoding the tyrosinase responsible for melanin synthesis revealed that a second gene in that operon encodes a protein, PpoB2, which is involved in copper transfer to tyrosinase. This finding made PpoB2 the first protein in the COG5486 group to which a physiological role has been assigned. Another enzyme of interest described in M. mediterranea is a multicopper oxidase encoding a membrane-associated enzyme that shows oxidative activity on a wide range of substrates typical of both laccases and tyrosinases. Finally, an enzyme very specific for L-lysine, which oxidises this amino acid in epsilon position and that has received a new EC number (1.4.3.20), has also been described for M. mediterranea. Overall, the studies carried out on this bacterium illustrate the power of exploring the physiology of selected microorganisms to discover novel enzymes of biotechnological relevance.

Isolation and cDNA cloning of an antibacterial L-amino acid oxidase from the skin mucus of the great sculpin Myoxocephalus polyacanthocephalus

The skin mucus of the great sculpin Myoxocephalus polyacanthocephalus showed both antibacterial and L-amino acid oxidase (LAO) activities. Antibacterial LAOs were purified from the skin mucus of the M. polyacanthocephalus by column chromatography and named MPLAO1, MPLAO2, and MPLAO3, based on the order of elution by ion-exchange high performance liquid chromatography. cDNA cloning of MPLAO3 revealed that the full-length cDNAwas 2659 bp and encoded the signal peptide (Met1-Ala26) and the mature protein (Val28-Phe520). A homology search using the BLAST program revealed that MPLAO3 shared sequence identity with LAO family proteins, and had 74% identity with the antibacterial LAO from the skin mucus of the rockfish Sebastes schlegeli. MPLAO3 catalyzed the oxidation of only L-lysine with a Km of 0.16 mM. MPLAO3 exhibited potent antibacterial activity against both Gram-positive and Gramnegative bacteria, and was most active against Aeromonas salmonicida JCM7874 with a minimum inhibitory concentration of 0.02 microg/mL. The antibacterial activity was attributable to H2O2, because the activity was completely lost in the presence of catalase. The antibacterial LAOs may be involved in the innate immunity of the great sculpin M. polyacanthocephalus skin.