Tyrosinase is a multi-copper enzyme which is widely distributed in different organisms and plays an important role in the melanogenesis and enzymatic browning. Therefore, its inhibitors can be attractive in cosmetics and medicinal industries as depigmentation agents and also in food and agriculture industries as antibrowning compounds. For this purpose, many natural, semi-synthetic and synthetic inhibitors have been developed by different screening methods to date. This review has focused on the tyrosinase inhibitors discovered from all sources and biochemically characterised in the last four decades.

https://northumbria-test.eprints-hosting.org/id/document/268389

A comprehensive review on tyrosinase inhibitors.

Inhibitory kinetics and mechanism of kaempferol on α-glucosidase

Studying non-covalent drug-DNA interactions.

α-Glucosidase inhibition by luteolin: kinetics, interaction and molecular docking.

Background Food antioxidants play a critical role in the food industry, and have become one of the most widespread methods of conserving food. Their cheapness and ease of use have made them a part of virtually all foodstuffs. Although different, all groups of food antioxidants have a same common objective, to conserve food for the longest possible time without altering it, conferring taste or color. Consumer trends have shifted the industry to find natural antioxidants for conservation, and although synthetic additives have been the mainstream, their natural counterparts have been gaining interest. Scope and approach This review focuses of the different antioxidant groups, describing their properties, function and applicability, as well as indexing the relevant legislation in order to be a guide for academia and industry. Key findings and conclusions The wide number of antioxidant additives allowed by the different countries if of synthetic origin, and consist of pure molecules. Although consumers are leaning toward natural additives, this offer is still quite limited despite the permission of rosemary extract within the European Union. There is still much work to be done in order to completely demystify the importance and safety of antioxidants as well as to harmonize legislation worldwide.

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Antioxidants: Reviewing the chemistry, food applications, legislation and role as preservatives

Xanthine oxidase (XO), a key enzyme in purine catabolism, is widely distributed in human tissues. It can catalyze xanthine to generate uric acid and cause hyperuricemia and gout. Inhibition kinetics assay showed that kaempferol inhibited XO activity reversibly in a competitive manner. Strong fluorescence quenching and conformational changes of XO were found due to the formation of a kaempferol-XO complex, which was driven mainly by hydrophobic forces. The molecular docking further revealed that kaempferol inserted into the hydrophobic cavity of XO to interact with some amino acid residues. The main inhibition mechanism of kaempferol on XO activity may be due to the insertion of kaempferol into the active site of XO occupying the catalytic center of the enzyme to avoid the entrance of the substrate and inducing conformational changes of XO. In addition, luteolin exhibited a stronger synergistic effect with kaempferol than did morin at the lower concentration.

Novel insights into the inhibitory mechanism of kaempferol on xanthine oxidase.

The binding mechanism of molecular interaction between diosmetin and human serum albumin (HSA) in a pH 7.4 phosphate buffer was studied using atomic force microscopy (AFM) and various spectroscopic techniques including fluorescence, resonance light scattering (RLS), UV–vis absorption, circular dichroism (CD), and Fourier transform infrared (FT–IR) spectroscopy. Fluorescence data revealed that the fluorescence quenching of HSA by diosmetin was a static quenching procedure. The binding constants and number of binding sites were evaluated at different temperatures. The RLS spectra and AFM images showed that the dimension of the individual HSA molecules were larger after interaction with diosmetin. The thermodynamic parameters, ΔH° and ΔS° were calculated to be −24.56 kJ mol–1 and 14.67 J mol–1 K–1, respectively, suggesting that the binding of diosmtin to HSA was driven mainly by hydrophobic interactions and hydrogen bonds. The displacement studies and denaturation experiments in the presence of urea indicate...

Probing the binding of the flavonoid diosmetin to human serum albumin by multispectroscopic techniques.

The flavonoid family has been reported to possess a high potential for inhibition of xanthine oxidase (XO). This study concerned the structural aspects of inhibitory activities and binding affinities of flavonoids as XO inhibitors. The result indicated that the hydrophobic interaction was important in the binding of flavonoids to XO, and the XO inhibitory ability increased generally with increasing affinities within the class of flavones and flavonols. The planar structure and the C2═C3 double bonds of flavonoids were advantageous for binding to XO and for XO inhibition. Both the hydroxylation on ring B and the substitution at C3 were unfavorable for XO inhibition more profoundly than their XO affinity. The methylation greatly reduced the inhibition (0.75–3.07 times) but hardly affected the affinity. The bulky sugar substitutions of flavonoids decreased the inhibition (1.69–1.99 times) and lowered the affinities (4.20–9.22 times) to different degrees depending on the conjunction site.

Dietary Flavonoids as Xanthine Oxidase Inhibitors: Structure-Affinity and Structure-Activity Relationships.

The interaction of indigo carmine (IC) with calf thymus DNA in physiological buffer (pH 7.4), using ethidium bromide (EB) dye as a fluorescence probe, was investigated by ultraviolet–visible absorption, fluorescence, and circular dichroism (CD) spectroscopy, coupled with viscosity measurements and DNA-melting studies. Hypochromicity of the absorption spectra of IC and enhancement in fluorescence polarization of IC were observed with the addition of DNA. Moreover, the binding of IC to DNA was able to decrease iodide and single-stranded DNA (ssDNA) quenching effects, increase the melting temperature and relative viscosity of DNA, and induce the changes in CD spectra of DNA. All of the evidence indicated that IC interacted with DNA in the mode of intercalative binding. Furthermore, the three-way synchronous fluorescence spectra data obtained from the interaction between IC and DNA–EB were resolved by parallel factor analysis (PARAFAC), and the results provided simultaneously the concentration information and...

Junhui Pan

Papers

Novel insights into the inhibitory mechanism of kaempferol on xanthine oxidase.

Probing the binding of the flavonoid diosmetin to human serum albumin by multispectroscopic techniques.

Dietary Flavonoids as Xanthine Oxidase Inhibitors: Structure-Affinity and Structure-Activity Relationships.

Spectroscopic studies of DNA interactions with food colorant indigo carmine with the use of ethidium bromide as a fluorescence probe.

Inhibition of chrysin on xanthine oxidase activity and its inhibition mechanism