Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.10.3.1 (tyrosinase)
9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A substrate recycling assay for phenolic compounds was developed using tyrosinase, a copper-containing enzyme, in excess NADH. The reaction of various phenols with the enzyme produced an o-quinone, which was then detected by recycling between reactions with the enzyme and NADH. The recycling of quinones by excess NADH to their original reduced forms prevented the problems of subsequent quinone polymerization and product inactivation which occur in nonrecycling assays. Absorbance measurements of the NADH consumption rate enhanced the assay sensitivity for catechol 100-fold compared to nonrecycling o-quinone detection, giving a detection limit of 240 nM. Fluorescence NADH monitoring permitted a 10-fold improvement over absorbance, with a detection limit of 23 nM. The recycling reaction was selective for o-quinones, and no interference was noted for p-quinones or quinoneimines. The two-step oxidation of phenols was observed as an initial lag phase (ca. 10 min), requiring a higher enzyme concentration to achieve the same sensitivity as that for catechol. The procedure was most useful for assaying catechol, 4-chlorocatechol, phenol, p-cresol, and 4-chlorophenol and may provide selective detection of these components in mixtures. Several other derivatives of catechols, including amine derivatives, were also detected, with relative sensitivity being related to substrate activity of the enzyme.
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PMID:A substrate recycling assay for phenolic compounds using tyrosinase and NADH. 785 38

The design of a new tyrosinase biosensor with improved stability and sensitivity is reported. The biosensor design is based on the construction of a graphite-Teflon composite electrode matrix in which the enzyme and colloidal gold nanoparticles are incorporated by simple physical inclusion. Experimental variables such as the colloidal gold loading into the composite matrix, the enzyme loading and the potential applied to the bioelectrode were optimized. The Tyr-Au(coll)-graphite-Teflon biosensor exhibited suitable amperometric responses at -0.10 V for the different phenolic compounds tested (catechol; phenol; 3,4-dimethylphenol; 4-chloro-3-methylphenol; 4-chlorophenol; 4-chloro-2-methylphenol; 3-methylphenol and 4-methylphenol). The limits of detection obtained were 3 nM for catechol, 3.3 microM for 4-chloro-2-methylphenol, and approximately 20 nM for the rest of phenolic compounds. The presence of colloidal gold into the composite matrix gives rise to enhanced kinetics of both the enzyme reaction and the electrochemical reduction of the corresponding o-quinones at the electrode surface, thus allowing the achievement of a high sensitivity. The biosensor exhibited an excellent renewability by simple polishing, with a lifetime of at least 39 days without apparent loss of the immobilized enzyme activity. The usefulness of the biosensor for the analysis of real samples was evaluated by performing the estimation of the content of phenolic compounds in water samples of different characteristics.
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PMID:Development of a high analytical performance-tyrosinase biosensor based on a composite graphite-Teflon electrode modified with gold nanoparticles. 1656 98

A novel method has been developed to immobilize tyrosinase onto the surface of boron-doped diamond (BDD) electrode. The hydrogen-terminated BDD (HBDD) surface was first functionalized by photochemically linking vinyl groups of allylamine, producing covalently linked amine-terminated active BDD (ABDD) surface. Then the tyrosinase was immobilized onto the ABDD surface by carbodiimide coupling reaction. The amperometric response was measured as a function of concentration of phenolic compounds in 0.1M phosphate buffer solution (pH 6.5). The tyrosinase-modified ABDD electrode gave a linear response range of 1-175, 1-200 and 1-200 microM and sensitivity of 80.0, 181.4 and 110.0 mA M(-1)cm(-2) for phenol, p-cresol, 4-chlorophenol, respectively. Moreover, selective detection of dopamine (DA) in the presence of ascorbic acid (AA) has been demonstrated with the tyrosinase-modified ABDD electrode. Linearity was observed within the range of 5-120 microM. The above enzyme electrode could maintain 90% of its original activity after intermittent use for 1 month when storing in a dry state at 4 degrees C.
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PMID:Amperometric biosensor based on tyrosinase immobilized on a boron-doped diamond electrode. 1662 10

The fabrication and performance of a reticulated vitreous carbon (RVC)-based tyrosinase flow-through electrode, in which the enzyme was covalently immobilized, is reported. The bioelectrode was tested as an amperometric detector for phenolic compounds. Variables affecting the construction of the enzyme flow-through electrode such as the RVC chemical pretreatment procedure, the enzyme immobilization method in the RVC matrix, the enzyme loading and the pH value of the buffer solution used, were optimized by flow-injection with amperometric detection. A good immobilization of the enzyme in the RVC matrix, in spite of the hydrodynamic conditions, was found. The same tyrosinase-RVC electrode could be used with no significant loss of the amperometric response for around 20 days, and reproducible responses could be achieved with different electrodes constructed in the same manner. Moreover, the operational stability of the bioelectrode was tested under continuous monitorization conditions. Calibration plots by flow injection with amperometric detection at -0.20 V were obtained for phenol, 2,4-dimethylphenol; 3-chlorophenol; 4-chlorophenol; 4-chloro-3-methylphenol and 2-aminophenol, with detection limits ranging from 2 mug l(-1) (4-chloro-3-methylphenol) to 2 mg l(-1).
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PMID:Detection of phenolic compounds in flow systems based on tyrosinase-modified reticulated vitreous carbon electrodes. 1896 60

An enzyme biosensor for the determination of 4-chlorophenol in water solutions based on potentiometric pH-sensitive field-effect transistors as semiconductor transducer and tyrosinase immobilised in saturated glutaraldehyde vapours as biorecognition element has been described for the first time. The main analytical characteristics were studied under different conditions, as well as the possibility to optimise these working parameters. Different factors, such as pH of immobilisation, the enzyme loading and time of immobilisation in glutaralaldehyde vapours were investigated with regard to the influence on sensitivity, limit of detection, dynamic range, and operational and storage stability. The best result gives a limit of detection close to 20 ppm and a dynamic range from 25 to 1000 ppm with sensitivity 2 mV mM(-1). The operational stability was not less-than15 h and the R.S.D. were approximately 3% for intra-sensors responses and approximately 7% for inter-sensors responses. The storage stability was >15 days.
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PMID:Development of tyrosinase biosensor based on pH-sensitive field-effect transistors for phenols determination in water solutions. 1896 37

The determination of diuron, atrazine, desisopropylatrazine (DIA) and desethylatrazine (DEA) were investigated using conductometric tyrosinase biosensor. Tyrosinase was immobilised on the biosensor sensitive part by allowing it to mix with bovine serum albumin (BSA) and then cross-linking in saturated glutaraldehyde (GA) vapour for 30min. The determination of pollutants in a solution was performed by comparison of the output signal (i.e percentage of the enzymatic activity) of the biosensor before and after contact with pollutants. The measurement of the enzymatic activity was performed using 4-chlorophenol, phenol and catechol substrates and response times ranging from 1 to 5min were observed. A 4-chlorophenol substrate was used to detect pesticides. A 30min contact time of the biosensor in the pollutant solution was used. Under the experimental conditions employed, detection limits for diuron and atrazine were about 1ppb and dynamic range of 2.3-2330 and 2.15-2150ppb were obtained for diuron and atrazine, respectively. A relative standard deviation (n=3) of the output signal was estimated to be 5% and a slight drift of 1.5muSh(-1) was observed. The 90% of the enzyme activity was still maintained after 23 days of storage in a buffer solution at 4 degrees C.
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PMID:Conductometric tyrosinase biosensor for the detection of diuron, atrazine and its main metabolites. 1896 41

In this paper, it is demonstrated that a single-receptor biosensor can be used to quantitatively determine each analyte in binary mixtures using multivariate data analysis tools based on the dynamic responses received from flow injection peaks. Mixtures with different concentrations of two phenolic compounds, catechol and 4-chlorophenol, were measured with a graphite electrode modified with tyrosinase enzyme at an applied potential of -50mV versus Ag/AgCl. A correction algorithm based on measurements of references in-between samples was applied to compensate for biosensor ageing as well as differences caused by deviations between biosensor preparations. After correction, the relative prediction errors with partial least squares regression (PLS-R) for catechol and 4-chlorophenol were 7.4 and 5.5%, respectively, using an analysis sequence measured on one biosensor. Additional validation mixtures of the two phenols were measured with a new biosensor, prepared with the same procedure but with a different batch of tyrosinase enzyme. Using the mixture responses for the first sensor as a calibration set in PLS-R, the relative prediction errors of the validation mixtures, after applying correction procedures, were 7.0% for catechol and 16.0% for 4-chlorophenol. These preliminary results indicate that by applying correction algorithms it could be possible to use less stable biosensors in continuous on-line measurements together with multivariate data analysis without time-consuming calibration procedures.
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PMID:Multivariate data analysis of dynamic amperometric biosensor responses from binary analyte mixtures-application of sensitivity correction algorithms. 1896 99

A novel tyrosinase biosensor based on biofuncational ZnO nanorod microarrays on the boron-doped nanocrystalline diamond (BDND) substrates was developed. The ZnO nanorod microarrays were firstly deposited on BDND thin film surfaces via a low-temperature solution method, and then ZnO nanorods were functionalized with the mixture of 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) by a co-condensation approach, then tyrosinase was immobilized to amino-modification ZnO nanorod surfaces by the covalent binding. As-prepared tyrosinase biosensors were used for the detection of phenolic compounds. The tyrosinase-modified BDND electrode gave a linear response range of 1-175, 1-150 and 1-150 microM and sensitivity of 576.2, 339.3 and 287.1 microA mmol(-1) cm(-2) for p-cresol, 4-chlorophenol and phenol, respectively. The low detection limit was estimated to be 0.1, 0.25 and 0.2 microM (s(b)/m=3), respectively. Therefore, the biofunctional ZnO nanorod arrays have potential applications as platforms to immobilize other enzymes and bioactive molecules in biosensors.
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PMID:A novel tyrosinase biosensor based on biofunctional ZnO nanorod microarrays on the nanocrystalline diamond electrode for detection of phenolic compounds. 1923 Jul 93

Tyrosinase (TYR) was covalently immobilized onto amino-functionalized carbon felt (CF) surface via eight different coupling reagents. Prior to the TYR-immobilization, primary amino group was introduced to the CF surface by the treatment with 3-aminopropyltriethoxysilane (APTES). The APTES modification of the CF surface was confirmed by XPS and SEM measurements. The terminal amino groups on the CF surface were cross-linked with protein lysine group (or cysteine group) using various coupling reagents. The resulting TYR-immobilized CF (TYR-CF) was utilized as a working electrode unit of a biocatalytic enzymatic flow-through detector. Catechol and 4-chlorophenol (4-CP) were used as model analytes for the evaluation of catecholase activity and phenolase activity, respectively, and flow injection peaks based on the electro-reduction of the enzymatically produced o-quinone species were monitored at -0.05 V vs. Ag/AgCl. Among eight coupling reagents, glutaraldehyde (GA) exhibited the best results on the sensitivity, the operational stability and the storage stability. The detection limits of catechol and 4-CP obtained by the GA-coupling method were found to be 6.0 x 10(-9)M and 1.5 x 10(-8)M, respectively with the sample through-put of 36 samples/h. No serious degradation of the peak current was observed over 30 consecutive samples injections on the GA-coupling method, while gradual decrease in the peak currents was observed on other seven coupling reagents. The GA-coupling method showed the best results on the storage stability, and 85% of original activity for catechol oxidation remained after 25 days storage.
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PMID:Carbon felt-based biocatalytic enzymatic flow-through detectors: chemical modification of tyrosinase onto amino-functionalized carbon felt using various coupling reagents. 1961 22

An amperometric biosensor was constructed by using ZnO nanorod clusters as platforms for immobilizing tyrosinase on the nanocrystalline diamond (NCD) electrodes. The results showed that ZnO nanorod clusters provided an advantageous microenvironment due to their favorable isoelectric point (IEP) for tyrosinase loading; immobilized tyrosinase generally retained its activity. The tyrosinase/ZnO/NCD electrode showed a linear response range of 1-210 and sensitivity of 179.9 microA mmol(-1) cm(-2) for p-cresol. The corresponding values were 1-190 and 90.2 for phenol, and 1-250 and 121.3 for 4-chlorophenol. The low detection limits were estimated to be 0.2 microM for p-cresol, 0.5 microM for phenol, and 0.4 microM for 4-chlorophenol (S/N = 3). The prepared enzyme electrode could keep 85% of its original activity after intermittent use for 4 weeks when stored in a dry state at 277 K. Therefore, the ZnO nanorod cluster thin films have potential applications as platforms to immobilize other enzymes and bioactive molecules in biosensors.
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PMID:A tyrosinase biosensor based on ZnO nanorod clusters/nanocrystalline diamond electrodes for biosensing of phenolic compounds. 1974 34


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