Determination of plasma and serum l-lysine using l-lysine ε-oxidase from Marinomonas mediterranea NBRC 103028T

Aggregation-induced emission enhancement of gold nanoclusters triggered by sodium heparin and its application in the detection of sodium heparin and alkaline amino acids

This work first reported that sodium heparin could cause the aggregation-induced emission enhancement (AIEE) effect of GSH-AuNCs (Glutathione functionalized gold nanoclusters). While it was interestingly found that the addition of alkaline amino acids would greatly weaken this effect. Thus, fluorescent system was designed for the quantitative detection of sodium heparin and alkaline amino acids. Negatively charged sodium heparin would connect with GSH-AuNCs through electrostatic attraction, leading to a significant AIEE effect. Then alkaline amino acids would competitively bind with sodium heparin, causing this effect to almost disappear. The reasons were as follows: (I) The hydrogen bonding between sodium heparin and alkaline amino acids was much stronger than electrostatic force, causing GSH-AuNCs to be competitively replaced. (II) Alkaline amino acids and GSH-AuNCs were both positively charged and repelled each other. The presence of alkaline amino acids would hinder the AIEE effect. (III) AIEE effect was confirmed to have a close relationship with the pH value which could be greatly affected by alkaline amino acids. (Ⅳ) Not only the hydrogen bonding, the electrostatic force also existed between the alkaline amino acids and sodium heparin. All the above reasons worked together to weaken the AIEE effect of GSH-AuNCs triggered by sodium heparin. Finally, both sodium heparin and alkaline amino acids were accurately detected, showing good correlation coefficients of 0.99 with the LODs of 0.0100 mg/mL (sodium heparin), 1.05 μM (histidine), 3.38 μM (arginine) and 6.16 μM (lysine), respectively.

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.

Screening and development of enzymes for determination and transformation of amino acids

The high stereo- and substrate specificities of enzymes have been utilized for micro-determination of amino acids. Here, I review the discovery of l-Phe dehydrogenase and its practical use in the diagnosis of phenylketonuria in more than 5,400,000 neonates over two decades in Japan. Screening and uses of other selective enzymes for micro-determination of amino acids have also been discussed. In addition, novel enzymatic assays with the systematic use of known enzymes, including assays based on a pyrophosphate detection system using pyrophosphate dikinase for a variety of l-amino acids with amino-acyl-tRNA synthetase have been reviewed. Finally, I review the substrate specificities of a few amino acid-metabolizing enzymes that have been altered, using protein engineering techniques, mainly for production of useful chemicals, thus enabling the wider use of natural enzymes.

L-Arginine oxidase from Pseudomonas sp. TPU 7192: Characterization, gene cloning, heterologous expression, and application to L-arginine determination

L-Arginine oxidase (AROD, EC 1.4.3.-) was discovered in newly discovered Pseudomonas sp. TPU 7192 and its characteristics were described. The molecular mass (MS) of the enzyme was estimated to be 528 kDa, which was accounted for by eight identical subunits with MS of 66 kDa each. AROD was identified as a flavin adenine dinucleotide (FAD)-dependent enzyme with 1 mol of FAD being contained in each subunit. It catalyzed the oxidative deamination of L-arginine and converted L-arginine to 2-ketoarginine, which was non-enzymatically converted into 4-guanidinobutyric acid when the hydrogen peroxide (H2O2) formed by L-arginine oxidation was not removed. In contrast, 2-ketoarginine was present when H2O2was decomposed. AROD was specific to L-arginine with a Km value of 149 μM. It exhibited maximal activity at 55 °C and pH 5.5. AROD was stable in the pH range 5.5-7.5 and >95% of its original activity was below 60 °C at pH 7.0. Since these enzymatic properties are considered suitable for the determination of L-arginine, the gene was cloned and expressed in a heterologous expression system. We herein successfully developed a new simple enzymatic method for the determination of L-arginine using Pseudomonas AROD.

Heterologous production of l-lysine ε-oxidase by directed evolution using a fusion reporter method

For the heterologous production of l-lysine ε-oxidase (LodA), we constructed a new plasmid carrying LodA gene fused in-frame with an antibiotic (phleomycine) resistant gene. The new plasmid was randomly mutated and the mutated plasmids were transformed into Escherichia coli BL21 (DE3) harboring lodB, which encodes a protein (LodB) acting in posttranslational modification of LodA, and active mutants were selected by phleomycin resistance and oxidase activities. One soluble LodA variant isolated by this method contained six silent mutations and one missense mutation. At these mutation points, the codon adaptations at Lys92, Ala550, and Thr646, and the amino acid substitution at His286 to Arg contributed to the production of its functional form. The active form of LodA variant was induced by post-modification of LodB in the heterologous coexpression, and the activity increased with additional NaCl and heat treatment. This is the first report of heterologous production of LodA by random mutagenesis.

Characterization of a pyridoxal-5'-phosphate-dependent l-lysine decarboxylase/oxidase from Burkholderia sp. AIU 395

A novel enzyme, which catalyzed decarboxylation of l-lysine into cadaverine with release of carbon dioxide and oxidative deamination of l-lysine into l-2-aminoadipic 5-semialdehyde with release of ammonia and hydrogen peroxide, was found from a newly isolated Burkholderia sp. AIU 395. The enzyme was specific to l-lysine and did not exhibit enzyme activities for other l-amino acids, l-lysine derivatives, d-amino acids, and amines. The apparent Km values for l-lysine in the oxidation and decarboxylation reactions were estimated to be 0.44 mM and 0.84 mM, respectively. The molecular mass was estimated to be 150 kDa, which was composed of two identical subunits with molecular mass of 76.5 kDa. The enzyme contained one mol of pyridoxal 5'-phosphate per subunit as a prosthetic group. The enzyme exhibiting decarboxylase and oxidase activities for l-lysine was first reported here, while the deduced amino acid sequence was homologous to that of putative lysine decarboxylases from the genus Burkholderia.

Rapid and selective enzymatic assay for L-methionine based on a pyrophosphate detection system

An enzymatic assay for L-methionine was developed by coupling adenosylmethionine synthetase (AdoMetS) to a pyrophosphate (PP(i)) detection system, which was constructed using pyruvate, phosphate dikinase. To expand the use of this assay, the PP(i) detection system was embodied as three different forms, which allowed PP(i) to be measured by UV, visible, and fluorescent light detectors. The assay system was robust and could tolerate the addition of inorganic phosphate and ATP to the assay mixtures. L-Methionine could be accurately determined by coupling the PP(i) detection system and AdoMetS. This AdoMetS coupling assay was highly selective to L-methionine and exhibited no significant activity to other proteinaceous amino acids, ammonia, or urea, unlike conventional enzymatic assays for L-methionine. Spike and recovery tests showed that the AdoMetS assay could accurately and reproducibly determine increases in L-methionine in human plasma samples without any pretreatment to remove proteins and potentially interfering low-molecular-weight molecules. The high selectivity and robustness of the AdoMetS assay provide rapid and high-throughput analysis of L-methionine in various kinds of analytes.

LodB is required for the recombinant synthesis of the quinoprotein L-lysine-ε-oxidase from Marinomonas mediterranea

Marinomonas mediterranea is a marine gamma-proteobacterium that synthesizes LodA, a novel L-lysine-ε-oxidase (E.C. 1.4.3.20). This enzyme oxidizes L-lysine generating 2-aminoadipate 6-semialdehyde, ammonium, and hydrogen peroxide. Unlike other L-amino acid oxidases, LodA is not a flavoprotein but contains a quinone cofactor. LodA is encoded by an operon with two genes, lodA and lodB. In the native system, LodB is required for the synthesis of a functional LodA. In this study, we report the recombinant expression of LodA in Escherichia coli using vectors that allow its expression and accumulation in the cytoplasm. To reveal the L-lysine-ε-oxidase activity using the Amplex Red method for hydrogen peroxide detection, it is necessary to first remove the E. coli cytoplasmic catalases. The flavoprotein LodB is the only M. mediterranea protein required in the recombinant system for the generation of the cofactor of LodA. In the absence of LodB, LodA does not contain the quinone cofactor and remains in an inactive form. The results presented indicate that LodB participates in the posttranslational modification of LodA that generates the quinone cofactor.

X-ray crystallographic evidence for the presence of the cysteine tryptophylquinone cofactor in L-lysine ε-oxidase from Marinomonas mediterranea

We have determined the x-ray crystal structure of L-lysine ε-oxidase from Marinomonas mediterranea in its native and L-lysine-complex forms at 1.94- and 1.99-Å resolution, respectively. In the native enzyme, electron densities clearly indicate the presence of cysteine tryptophylquinone (CTQ) previously identified in quinohemoprotein amine dehydrogenase. In the L-lysine-complex, an electron density corresponding to the bound L-lysine shows that its ε-amino group is attached to the C6 carbonyl group of CTQ, suggesting the formation of a Schiff-base intermediate. Collectively, the present crystal structure provides the first example of an enzyme employing a tryptophylquinone cofactor in an amine oxidase.

Selective tryptophan determination using tryptophan oxidases involved in bis-indole antibiotic biosynthesis

A novel tryptophan assay was developed using tryptophan oxidases. Although many l-amino acid oxidases (LAAOs) have been reported to catalyze tryptophan oxidation, most of them have broad substrate specificity and oxidize multiple amino acids besides tryptophan. To obtain a tryptophan-specific LAAO, we focused on bis-indole antibiotic biosynthesis, a bacterial secondary metabolic pathway. A putative LAAO from Streptomyces sp. TP-A0274, StaO involved in staurosporine biosynthesis, was heterologously expressed, biochemically characterized, and shown to serve as a selective tryptophan oxidase for the first time. In addition, another LAAO, VioA involved in violacein biosynthesis in Chromobacterium violaceum, was characterized for comparison with StaO. Interestingly, StaO and VioA share similar properties, namely narrow substrate specificity and high affinity for l-tryptophan, despite the phylogenetic distance between these enzymes. Owing to these features, uncommon among known LAAOs, StaO and VioA assays can be used for selective and accurate quantification of l-tryptophan via a coupled colorimetric reaction. Indeed, StaO and VioA assays provided tryptophan concentrations in human plasma as accurately as those obtained by high-performance liquid chromatography. Therefore, these enzymes were clearly shown to offer an effective method for determining tryptophan in biological samples rapidly, inexpensively, and accurately. The results shown here also suggest the possibility of metabolism-oriented screening as a strategy to obtain enzymes highly selective for individual biomolecules.