Study of tyrosine and dopa enantiomers as tyrosinase substrates initiating L‐ and D‐melanogenesis pathways

Tyrosinase starts melanogenesis and determines its course, catalyzing the oxidation by molecular oxygen of tyrosine to dopa, and that of dopa to dopaquinone. Then, nonenzymatic coupling reactions lead to dopachrome, which evolves toward melanin. Recently, it has been reported that d‐tyrosine acts as tyrosinase inhibitor and depigmenting agent. The action of tyrosinase on the enantiomers of tyrosine (l‐tyrosine and d‐tyrosine) and dopa (l‐dopa and d‐dopa) was studied for the first time focusing on quantitative transient phase kinetics. Post‐steady‐state transient phase studies revealed that l‐dopachrome is formed more rapidly than d‐dopachrome. This is due to the lower values of Michaelis constants for l‐enantiomers than for d‐enantiomers, although the maximum rates are equal for both enantiomers. A deeper analysis of the inter‐steady‐state transient phase of monophenols demonstrated that the enantiomer d‐tyrosine causes a longer lag period and a lower steady‐state rate, than l‐tyrosine at the same concentration. Therefore, d‐melanogenesis from d‐tyrosine occurs more slowly than does l‐melanogenesis from l‐tyrosine, which suggests the apparent inhibition of melanin biosynthesis by d‐tyrosine. As conclusion, d‐tyrosine acts as a real substrate of tyrosinase, with low catalytic efficiency and, therefore, delays the formation of d‐melanin

Uso de recursos digitales en la docencia virtual de asignaturas STEM en Foundation Courses durante el confinamiento

The lockdown caused by COVID-19 led to the adoption of new virtual methodologies using digital tools. The aim of this study was to design and validate a questionnaire on the use of digital media in the virtual teaching of STEM subjects in Foundation Courses. For this purpose, a descriptive non-experimental quantitative design was used and, with the administration of the designed questionnaire, data were collected from 61 students enrolled in these courses during the academic year 2021/2022 at Northumbria University (United Kingdom). The results showed that the reliability and internal consistency of the implemented questionnaire were good (Cronbach's Alpha = .78; Composite Reliability = .79; Mean Extracted Variance = .48; Omega = .95; KMO = .64) and that in general the student body stated that they had good access to and use of digital media and smooth communication with lecturers during the placement. In addition, they stated that they had adapted favourably to virtual teaching and that they had successfully acquired subject competences. The pandemic has brought about the implementation of these new methodologies and has meant a renewal and implementation of new resources, with the consequent acquisition of digital competences by both teaching staff and students.El confinamiento provocado por la COVID-19 supuso la adopción de metodologías docentes virtuales aplicadas a través del uso de herramientas digitales. El objetivo del presente trabajo fue diseñar y validar un cuestionario sobre el uso de los medios digitales en la docencia virtual de las asignaturas STEM de los Foundation Courses. Para ello, se empleó un diseño cuantitativo descriptivo no experimental y, con la administración del cuestionario diseñado, se recogieron datos de 61 estudiantes matriculados en estos cursos durante el curso académico 2021/2022 en la Universidad de Northumbria (Reino Unido). Los resultados mostraron que la fiabilidad y consistencia interna del cuestionario implementado fueron buenas (Alfa de Cronbach = .78; Fiabilidad compuesta = .79; Varianza Media Extractada = .48; Omega = .95; KMO = .64) y que en general el alumnado afirmó que tuvo un buen acceso y uso de los medios digitales, y una fluida comunicación con el profesorado durante el confinamiento. Además, manifestó que se había adaptado favorablemente a la docencia virtual y que había adquirido satisfactoriamente las competencias de las asignaturas. La pandemia ha consolidado la implementación de estas nuevas metodologías que han supuesto una renovación e implementación de nuevos recursos, con la consiguiente adquisición y mejora de las competencias digitales tanto por parte del profesorado como por parte del alumnado

Blood parameters as biomarkers in a Salmonella spp. disease model of weaning piglets

peer-reviewedBackground The weaning pig is used as an experimental model to assess the impact of diet on intestinal health. Blood parameters (BP) are considered a useful tool in humans, but there is very scarce information of such indicators in the weaning pig. The objective of the present study is to evaluate the use of different BP as indicators in an experimental model of salmonellosis. Methodology Seventy-two 28-day-old piglets were divided into four groups in a 2x2 factorial arrangement, with animals receiving or not a probiotic combination based on B. infantis IM1® and B. lactis BPL6 (109 colony forming units (cfu)/d) and orally challenged or not a week later with Salmonella Typhimurium (5x108 cfu). Blood samples of one animal per pen (N = 24) were taken four days post-inoculation for the evaluation of different BP using an I-stat® System and of plasmatic concentrations of zinc, iron and copper. Principal findings Results reported marginal deficiencies of zinc in piglets at weaning. Moreover, plasmatic zinc, copper and iron presented good correlations with weight gain (r 0.57, r -0.67, r 0.54 respectively; P < 0.01). Blood electrolytes (Na+, Cl- and K+) decreased (P < 0.01) only when the performance of the animals was seriously compromised and clinical symptoms were more apparent. Acid-base balance parameters such as HCO3-, TCO2 and BEecf significantly correlated with weight gain, but only in the challenged animals (r -0.54, r -0.55, and r -0.51, respectively; P < 0.05), suggesting metabolic acidosis depending on Salmonella infection. Glucose was affected by the challenge (P = 0.040), while Htc and Hgb increased with the challenge and decreased with the probiotic (P < 0.05). Furthermore, correlations of Glu, Htc and Hgb with weight gain were observed (P < 0.05). Overall, BP could be regarded as simple, useful indexes to assess performance and health of weaning piglets

CORRESPONDENCE BETWEEN PERSONALITY AND JOB TITLE

Does the position held by an individual in a company fit into his/her personality? The answer to this question is yes. This is because there is significant relationship between the characteristics possessed by a worker which includes his character, personality and way of life, with the current position he/she is holding in an organization. The evolution of man is in accordance with technological advancement, new cultures, social and economic developments, among other phenomena. In other words, the success in the position given to a person will depend largely on his/her personality from a mental and physical point of view. This aim of this paper is to analyze the part of clinical psychology which is associated with human talent through a series of characteristics and personality traits. Personality traits and characteristics are crucial for the proper performance of a worker in a specific job

Enzymatic oxidation of oleuropein and 3-hydroxytyrosol by laccase, peroxidase and tyrosinase.

The oxidation of oleuropein and 3‐hydroxytyrosol by oxidases laccase, tyrosinase, and peroxidase has been studied. The use of a spectrophotometric method and another spectrophotometric chronometric method has made it possible to determine the kinetic parameters Vmax and KM for each enzyme. The highest binding affinity was shown by laccase. The antioxidant capacities of these two molecules have been characterized, finding a very similar primary antioxidant capacity between them. Docking studies revealed the optimal binding position, which was the same for the two molecules and was a catalytically active position. Practical applications: One of the biggest environmental problems in the food industry comes from olive oil mill wastewater with a quantity of approximately 30 million tons per year worldwide. In addition, olive pomace, the solid residue obtained from the olive oil production, is rich in hydroxytyrosol and oleuropein and the action of enzymatic oxidases can give rise to products in their reactions that can lead to polymerization. This polymerization can have beneficial effects because it can increase the antioxidant capacity with potential application on new functional foods or as feed ingredients. Tyrosinase, peroxidase, and laccase are the enzymes degrading these important polyphenols. The application of a spectrophotometric method for laccase and a chronometric method, for tyrosinase and peroxidase, allowed us to obtain the kinetic information of their reactions on hydroxytyrosol and oleuropein. The kinetic information obtained could advance in the understanding of the mechanism of these important industrial enzymes

Kinetic characterization of the oxidation of catecolamines and related compounds by laccase

The pathways of melanization and sclerotization of the cuticle in insects are carried out by the action of laccases on dopamine and related compounds. In this work, the laccase action of Trametes versicolor (TvL) on catecholamines and related compounds has been kinetically characterized. Among them, dopamine, L-dopa, L-epinephrine, L-norepinephrine, DL-isoprenaline, L-isoprenaline, DL-α-methyldopa, L-α-methyldopa and L-dopa methylester. A chronometric method has been used, which is based on measuring the lag period necessary to consume a small amount of ascorbic acid, added to the reaction medium. The use of TvL has allowed docking studies of these molecules to be carried out at the active site of this enzyme. The hydrogen bridge interaction between the hydroxyl oxygen at C-4 with His-458, and with the acid group of Asp-206, would make it possible to transfer the electron to the T1 Cu-(II) copper centre of the enzyme. Furthermore, Phe-265 would facilitate the adaptation of the substrate to the enzyme through Π-Π interactions. To kinetically characterize these compounds, we need to take into consideration that, excluding L-dopa, L-α-methyldopa and DL-α-methyldopa, all compounds are in hydrochloride form. Because of this, first we need to kinetically characterize the inhibition by chloride and, after that, calculate the kinetic parameters K M and V max S. From the kinetic data obtained, it appears that the best substrate is dopamine. The presence of an isopropyl group bound to nitrogen (isoprenaline) makes it especially difficult to catalyse. The formation of the ester (L-dopa methyl ester) practically does not affect catalysis. The addition of a methyl group (α-methyl dopa) increases the rate but decreases the affinity for catalysis. L-Epinephrine and L-norepinephrine have an affinity similar to isoprenaline, but faster catalysis, probably due to the greater nucleophilic power of their phenolic hydroxyl

Test-Retest Reliability of Kinematic Parameters of Timed Up and Go in People with Type 2 Diabetes

Diabetes mellitus is a chronic disease defined as a state of hyperglycaemia in fasting or postprandial states. Patients with type 2 diabetes mellitus (T2DM) often show reduced physical function, including low levels of strength, balance or mobility. In this regard, the timed up and go (TUG) is a widely used physical fitness test in people with T2DM. However, there is a lack of studies evaluating the properties TUG in this population. The present study aimed to evaluate the test-retest reliability of kinetic and kinematic parameters obtained from TUG in the diabetic population with different levels of diabetic neuropathy. A total of 56 patients with T2DM participated in the study. They were divided into three groups according to the vibration threshold: (a) severe neuropathy, (b) moderate neuropathy and (c) normal perception. The TUG was performed using two force platforms to assess kinematic measurements. The results show that both kinetic and kinematic variables had good to excellent reliability. The reliability of TUG was excellent for the whole sample and the groups with non-severe neuropathy. However, it was just good for the group with severe neuropathy

BSSRDF estimation from single images

We present a novel method to estimate an approximation of the reflectance characteristics of optically thick, homogeneous translucent materials using only a single photograph as input. First, we approximate the diffusion profile as a linear combination of piecewise constant functions, an approach that enables a linear system minimization and maximizes robustness in the presence of suboptimal input data inferred from the image. We then fit to a smoother monotonically decreasing model, ensuring continuity on its first derivative. We show the feasibility of our approach and validate it in controlled environments, comparing well against physical measurements from previous works. Next, we explore the performance of our method in uncontrolled scenarios, where neither lighting nor geometry are known. We show that these can be roughly approximated from the corresponding image by making two simple assumptions: that the object is lit by a distant light source and that it is globally convex, allowing us to capture the visual appearance of the photographed material. Compared with previous works, our technique offers an attractive balance between visual accuracy and ease of use, allowing its use in a wide range of scenarios including off-the-shelf, single images, thus extending the current repertoire of real-world data acquisition techniques

Metal-Controlled Magnetoresistance at Room Temperature in Single-Molecule Devices

The appropriate choice of the transition metal complex and metal surface electronic structure opens the possibility to control the spin of the charge carriers through the resulting hybrid molecule/metal spinterface in a single molecule electrical contact at room temperature. The single molecule conductance of a Au/molecule/Ni junction can be switched by flipping the magnetization direction of the ferromagnetic electrode. The requirements of the molecule include not just the presence of unpaired electrons: the electronic configuration of the metal center has to provide occupied or empty orbitals that strongly interact with the junction metal electrodes and that are close in energy to their Fermi levels for one of the electronic spins only. The key ingredient for the metal surface is to provide an efficient spin texture induced by the spin orbit coupling in the topological surface states that results in an efficient spin-dependent interaction with the orbitals of the molecule. The strong magnetoresistance effect found in this kind of single-molecule wire opens a new approach for the design of room-temperature nanoscale devices based on spin-polarized currents controlled at molecular level

HPLC-PDA METHOD FOR THE QUANTIFICATION OF PARACETAMOL IN PLASMA: APPLICATION TO PK/PD STUDIES WITH ARTHRITIC RATS

Objective: To develop and validate an easy, rapid, sensitive and selective high-performance liquid chromatography with photodiode diode-array (HPLC-PDA) detection method for quantification of paracetamol and to demonstrate its application in a pharmacokinetic–pharmacodynamic study with arthritic rats.Methods: Paracetamol was separated from plasma samples (50-100 µl) by a single protein precipitation step, prior to HPLC-PDA detection. The separation was performed on a Knauer Eurospher II, C18 column 5 µm, 150 × 4.6 mm. The mobile phase comprised a mixture of water: methanol (75:25) and the flow rate was 1.1 ml/min. The detection wavelength was set at 245 nm. All analyses were carried out at room temperature (25 °C). Pharmacodynamics data were obtained with a gout-type pain model in rats.Results: The method was linear within a range of 0.2-200 µg/ml (R2≥0.99). The intra-day and inter-day precision and accuracy expressed as coefficient of variation and relative error, respectively were below 10%. The lower limit of quantification was 0.2 µg/ml. Plasma samples were stable at least for 5 w at ‒20° C.Conclusion: The validated method is sensitive, precise, accurate and specific as other more complex high-performance liquid chromatographic methods coupled to mass spectrometry (HPLC-MS), using small plasma samples (50-100 µl) and with a short time analysis (&lt;5 min). The method was successfully applied to a pharmacokinetic-pharmacodynamic study of paracetamol in arthritic rats.Â