1,721,017 research outputs found
Regulative aspects of the Kupffer cells tyrosinase from Rana esculenta L. The effects of melanin and H2O2on the DOPA-OXIDATION catalyzed by this enzime
No full textnovel tyrosinase-based biosensor!
No full textPhenolic derivatives determination in medical, food and environmental samples is very important because of the high toxicity of these compounds. Currently used phenol detection methods are neither inexpensive nor rapid screening techniques.
Tyrosinase-based biosensors have been proven to be promising tools for this purpose because of advantages such as selectivity, low cost, fast and cheap screening of samples. Many materials, such as different polymers, alumina sol-gels, magnetic nanoparticles-chitosan nanocomposite, have been employed to immobilize tyrosinase in biosensors. These compounds were used in electrochemical biosensors and the enzyme was immobilized on the electrode surface.
Moreover orderly protein films on a solid support can be prepared using a layer-by-layer assembly, a simple process based on the sequential adsorption of polyanions and polycations guided by electrostatic interactions. Using this technique, we obtained a mushroom tyrosinase/poly(dimethyldiallylammonium chloride) multilayer on a quartz support.
The catecholase activity of the immobilized enzyme was detected using L-DOPA as substrate. Dopachrome formation was revealed at 475 nm. The kinetic parameters (Km and Vmax) of the tyrosinase were determined and compared with the behaviour of the enzyme in solution.
Our results demonstrate for the first time that “layer by layer” deposition preserves the enzymatic properties of tyrosinase. For this reason we propose this layering method as a useful potential tool for the production of a tyrosinase-based biosensor
Bioactive paper platform for colorimetric phenols detection.
No full textPolyphenols, as food antioxidants, are of great interest due to their health benefits as they decrease the risks of cancer and coronary cardiopathy (1). Moreover they influence the quality and organoleptic characteristics of foods (2). Lastly, some neurotransmitters are phenolic compounds.
Hence the need to work out a sensitive, portable and inexpensive detection methods to monitor these compounds (3). We developed a disposable paper-based bioassay for the detection of phenolic compounds; the assay was successfully applied for the determination of polyphenols in a real matrix such as wine. The colorimetric quantification of the analyte is based on an enzymatic assay. The tyrosinase enzyme has been immobilized on a filter paper by simple over-spotting with 3-methyl-2-benzothiazolinone hydrazone (MBTH), that allows the detection of phenols by forming stable colored adducts with their enzymatic oxidation products. The color intensity of the adduct (developed after 5 min of reaction) was found to increase proportionally with the increase of the phenolic substrate concentrations. Analyte detection can be achieved by eye and quantification can be simply obtained by using a camera phone and an image analysis software.
The response, characteristics of the sensor were determined using l-3,4-dihydroxyphenyl-alanine (l-DOPA), an archetype substrate of tyrosinase, as the analyte.
This disposable paper-based biosensor relies on a rapid and simple method, without need of sophisticated instrumentation and trained personnel and could be extremely useful in remote locations or developing countries which does not have ready access to laboratory facilities and where simple, sensitive and low cost bioassays are essentials
The coupling between electron transfer and protein dynamics in the bacterial photosynthetic reaction center: trapping of conformational substates in room tenmperature amorphous matrices
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Mushroom Tyrosinase in Polyelectrolyte Multilayers as an Optical Biosensor for o-diphenols
No full textDetermination of phenolic derivatives is very important in medical, food and environmental samples
because of their relevant significance in health care and pollution monitoring. Tyrosinase-based biosensors
are promising tools for this purpose because of several advantages with respect to currently used
detection methods.
A key aspect in the development of a biosensor is the effective immobilization of the enzyme. In this
work, ordered tyrosinase films on an optical transparent support were immobilized by a “layer-by-layer”
(LbL) assembly, alternating the enzyme with the polycation polymer poly(dimethyldiallylammonium
chloride). As confirmed by UV–vis spectroscopy, the LbL deposition allowed a high loading of enzyme.
The immobilized tyrosinase functionality was proven and its kinetic parameters were spectrophotometrically
determined. The prepared biosensor was used to optically detect the o-diphenolic compound
l-3,4-dihydroxyphenyl-alanine (l-DOPA) and exhibited good repeatability and time stability. The sensing
properties of the system were studied by means of both absorption and fluorescence spectroscopy.
The bioassay based on the absorbance measurements gave a LOD of 23M and a linear response up to
350M. The bioassay based on the fluorescence measurements gave a LOD of 3Mand a linear response
in the range of tens of micromolar (the exact value depends on the number of mushroom tyrosinase
layers). Biosensor sensitivity could be modulated varying the number of the immobilized enzyme layers
Influence of anionic phospholipids on the functionality of QA and QB sites of the photosynthetic Reaction Centre from Rb. sphaeroides
No full textMETASTASI LINFONODALI AL COLLO DEI CARCINOMI CUTANEI DELL'ESTREMO CEFALICO: STUDIO CLINICO STATISTICO
No full textDimostrazione di una attività tirosinasica nelle cellule di Kupffer di Rana esculenta L. [Demonstration of a tyrosinase type activity in Kupffer cells of Rana esculenta L].
No full textMelanogenesis in the pigment cells of Rana esculenta L. liver: evidence for tyrosinase-like activity in the melanosome protein fraction
No full textThis work demonstrates the presence of a tyrosinase-like activity in the pigment cells of frog Rana esculenta L. liver. The activity was evidenced in the protein melanosome fraction extracted with differential centrifugation methods. The study of this activity, carried out with spectrophotometric methods, indicates 1) the system presents the characteristics of an allosteric enzyme; 2) the grade of cooperativity shows oscillations going from negative cooperativity toward the substrate, evident in the warmest months of the year, to an absence of cooperativity in the coldest months of the year; and 3) the levels of activity of the system also vary according to season, with the highest levels appearing in the coldest months of the year. Given that this extracutaneous system of pigment cells, different from melanocytes, is able to carry out melanogenesis, we suggest its inclusion in the classification of pigment cells
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