Search results for "Catechol"

Influence of the functionalisation of mesoporous silica material UVM-7 on polyphenol oxidase enzyme capture and enzymatic browning

2020

Polyphenol oxidase (PPO), also known as tyrosinase and catechol oxidase, is the enzyme responsible for enzymatic browning in foods. It causes undesirable organoleptic, nutritional and colour changes. Here, we report the preparation of five nanomaterials and a study of their ability to modulate PPO enzyme activity. The materials consist of UVM-7 supports (a mesoporous silica material) modified with diverse functional groups (i.e. amine, carboxylic acid, isocyanate, alkane and pyridine). We also studied the PPO immobilisation capability of the materials. All the materials, except the carboxylic acid functionalised one, offer high PPO loading capabilities and the immobilisation speed increases…

Gas chromatography/mass spectrometry of catechol estrogens

1992

Abstract Catecholestrogens (CCEs), namely 2- or 4-hydroxyestradiol and hydroxyestrone, are highly polar, reactive, and extremely labile estrogen metabolites in many experimental conditions. For these reasons, indirect assay methods mainly have been used. Some experimental evidence suggests that CCEs are synthesized and biologically active mostly in target cells. At this level, unfortunately, the indirect assays cannot be used. We present a method of gas Chromatographic/mass spectral (GC/MS) analysis for the identification of individual CCEs; the major fragmentation ions of authentic estrogen standards as trimethylsilylether derivatives, and the MS patterns of the major CCEs, namely, 2-hydro…

A new method for the cytochemical demonstration ofp-diphenol: O2 oxidoreductase (laccase)

1971

Nachweis des Enzymsp-Diphenol: O2 oxidoreductase (Laccase) in den Zellen der PilzeAspergillus fumigatus, Aureobasidium pullulans undNeurospora sitophila durch einen Azofarbstoff, der mittels Kupplung des enzymatisch gebildetenp-Chinons mitBesthorn's Hydrazon(3-Methyl-benzthiazolon(2)-hydrazon-hydrochlorid) entsteht. Als Substrat wird Hydrochinon verwendet. Der Farbstoff wird in runden, rotbraunen Granula abgelagert. Kontrollreaktionen bestatigen die Spezifitat der Reaktion.

Histamine inhibits spontaneous activity of the uterus of the progesterone-treated rat

1993

Cardiovascular effects of the methanol and dichloromethanol extracts fromTeucrium cartaginenses L.

1998

Methanol and dichloromethanol extracts of the leaves and stems of Teucrium cartaginensesL. have been tested for their effects on resting arterial blood pressure, heart rate and noradrenaline induced hypertension. Both extracts administered i.v. to urethane anaesthetized normotensive rats reduced mean arterial blood pressure and heart valve, while only the dichloromethanol extract prevented noradrenaline induced hypertension. © 1998 John Wiley & Sons, Ltd.

Reactive oxygen and ethylene are involved in the regulation of regurgitant-induced responses in bean plants.

2004

Summary Application of regurgitant from Leptinotarsa decemlineata Say on wound surfaces of one wounded leaf of intact bean ( Phaseolus vulgaris L.) plants resulted in activation of ethylene biosynthesis followed by an increase of both peroxidase and polyphenol oxidase activity. The aim of the present investigation was to study the source of increased oxidative enzyme activities in regurgitant-treated bean leaves and to determine if hydrogen peroxide and ethylene biosynthesis is responsible for regurgitant-induced amplification of wound responses in bean plants. As the regurgitant contained relative high activities of both peroxidase and polyphenol oxidase, there is a possibility that increa…

<i>In vitro</i> Modeling of Ryanodine Receptor 2 Dysfunction Using Human Induced Pluripotent Stem Cells

2011

Background/Aims: Induced pluripotent stem (iPS) cells generated from accessible adult cells of patients with genetic diseases open unprecedented opportunities for exploring the pathophysiology of human diseases in vitro. Catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1) is an inherited cardiac disorder that is caused by mutations in the cardiac ryanodine receptor type 2 gene (RYR2) and is characterized by stress-induced ventricular arrhythmia that can lead to sudden cardiac death in young individuals. The aim of this study was to generate iPS cells from a patient with CPVT1 and determine whether iPS cell-derived cardiomyocytes carrying patient specific RYR2 mutation recap…

Origin of the natural variation in the storage of dietary carotenoids in freshwater amphipod crustaceans

2020

16 pages; International audience; Carotenoids are diverse lipophilic natural pigments which are stored in variable amounts by animals. Given the multiple biological functions of carotenoids, such variation may have strong implications in evolutionary biology. Crustaceans such as Gammarus amphipods store large amounts of these pigments and inter-population variation occurs. While differences in parasite selective pressure have been proposed to explain this variation, the contribution of other factors such as genetic differences in the gammarid ability to assimilate and/or store pigments, and the environmental availability of carotenoids cannot be dismissed. This study investigates the relati…

Simultaneous determination of 4-nitroanisole, 4-nitrophenol, and 4-nitrocatechol by phase-sensitive ac polarography.

1977

Abstract Phase‐sensitive ac polarography was applied to the simultaneous quantitative determination of 4‐nitroanisole, 4‐nitrophenol and 4‐nitrocatechol in alkaline solutions. Certain experimental precautions are necessary to determine each compound in the presence of the other two. Thus, 4‐nitrocatechol is determined indirectly by forming a yellow ratio chelate with cupric ions, whereas 4‐nitroanisole is determined directly by the reduction waves of the nitro group. For the determination of 4‐nitrophenol, the interference by the simultaneously present 4‐nitrocatechol must be eliminated by masking it by the addition of magnesium ions. The method described permits a qualitative and quantitat…

Bioinspired catechol-terminated self-assembled monolayers with enhanced adhesion properties

2013

The role of the catechol moiety in the adhesive properties of mussel proteins and related synthetic materials has been extensively studied in the last years but still remains elusive. Here, a simplified model approach is presented based on a self-assembled monolayer (SAM) of upward-facing catechols thiol-bound to epitaxial gold substrates. The orientation of the catechol moieties is confirmed by spectroscopy, which also showed lack of significant amounts of interfering o-quinones. Local force-distance curves on the SAM measured by atomic force microscopy (AFM) shows an average adhesion force of 45 nN, stronger than that of a reference polydopamine coating, along with higher reproducibility …