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Free Radicals and Antioxidants
Published in Chuong Pham-Huy, Bruno Pham Huy, Food and Lifestyle in Health and Disease, 2022
Chuong Pham-Huy, Bruno Pham Huy
Chalcones are aromatic ketone, in which two aromatic rings are linked by a three carbon α, β-unsaturated carbonyl system. They are precursors of flavanones and other flavonoids by chalcone isomerase in plants. They include phloretin and phloridzin and are abundant in edible plants such as Chinese angelica (Angelica sinensis or Dong Quai), ashitaba (Angelica keiskei koidzumi) discovered in Japan, apples and peels, ciders, hops and beers. Ashitaba is a species of the celery family. Its stems have a thick yellow juice containing chalcones which is unique to this strain of angelica. Angelica herbs are considered to be anti-aging by Chinese and Japanese medicines (166). The chalcones in ashitaba are known as xanthoangelol, xanthoangelol-E, and 4-hydrooxyderricin, and were discovered by Japanese researchers. All chalcones are strong antioxidants and possess a wide range of biological activities: anti-inflammatory, analgesic, antiviral, antimicrobial, anti-malarial, anti-leishmanial, antiplatelet, anticancer, anti-obesity, anti-platelet, hypo-lipidemic, cardio-protective agents, anti-fungal, and more (166).
The Modification of Cysteine
Published in Roger L. Lundblad, Chemical Reagents for Protein Modification, 2020
Modification of cysteine with sodium tetrathionate (Figure 2)4 is similar to oxidation. This reaction has the advantage of ready reversibility by mild reducing agents. Reaction with sodium tetrathionate has been used to study cysteine in chalcone isomerase.5 The native enzyme was only slowly inactivated by sodium tetrathionate (pH 5.2 [50 mM MES], k2 <0.005 M−1 min−1; pH 7.5 [50 mM HEPES], k2 = 0.009 M−1 min−1; pH 9.4 [50 mM CHES], k2 = 0.093 M−1 min−1). In the presence of 6.0 M urea, the enzyme was rapidly inactivated (pH 7.5, k2 >690 M−1 min−1).
Formulated Natural Selective Estrogen Receptor Modulators: A Key To Restoring Women’s Health
Published in Megh R. Goyal, Durgesh Nandini Chauhan, Plant- and Marine-Based Phytochemicals for Human Health, 2018
A. Anita Margret, S. Aishwarya, J. Theboral
Isoflavones are naturally occurring isoflavonoids, which are the most studied class of phytoestrogens and are found almost exclusively in the family of Leguminosae.34 The flavonoids belong to large chemical class and are formed through the phenylpropanoid-acetate pathway by chalcone synthase and condensation reactions with malonyl-CoA. Isoflavones are produced through general phenylpropanoid pathway that produces flavonoid compounds in higher plants. The phenylpropanoid pathway begins from the amino acid phenylalanine, and an intermediate of the pathway, naringenin, is sequentially converted into the isoflavone genistein by two legume-specific enzymes: isoflavone synthase and a dehydratase. Similarly, another intermediate naringenin chalcone is converted to the isoflavone daidzein by sequential action of three legume-specific enzymes: chalcone reductase, type II chalcone isomerase, and isoflavone synthase. Plants use isoflavones and their derivatives as phytoalexin compounds to ward off disease-causing pathogenic fungi and other microbes. The isoflavonoids are subclass of flavonoids that differ in the position of one phenolic ring, which has shifted from C-3 to C-2. The isoflavonoids from legumes, that includes genistein-2 and daidzein, are most studied phytoestrogens. They can exist as glucosides or as glycones that are easily transported across intestinal epithelial cells and are hydrolyzed in the gut.46
A comprehensive review on phytochemistry, pharmacology, and flavonoid biosynthesis of Scutellaria baicalensis
Published in Pharmaceutical Biology, 2018
Zi-Long Wang, Shuang Wang, Yi Kuang, Zhi-Min Hu, Xue Qiao, Min Ye
The flavonoids in S. baicalensis Georgi possess various pharmacological activities. Their biosynthesis in the living plant has gained increasing attention in recent years. Zhao et al. systematically investigated the biosynthetic pathways of free flavones. The Scutellaria flavones are originally derived from phenylalanine, which is catalyzed by phenylalanine ammonia lyase (PAL) to form cinnamic acid. Interestingly, the subsequent biosynthetic steps were different for flavones in the aerial parts and in the roots (Figure 4). For the 4′-hydroxyl flavones, which are mainly distributed in the aerial parts, cinnamic acid is sequentially catalyzed by cinnamoyl 4 hydroxylase (C4H), p-coumaroyl CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), and flavone synthase (FNSII-1) to form apigenin (Zhao et al. 2016a, 2016b). Then apigenin is hydroxylated by flavone 6-hydroxylase (F6H) to generate scutellarein, as shown in Figure 5 (Zhao Q et al. 2018). The flavones in the roots, however, usually lack a 4′-OH group on the B-ring. For their biosynthesis, cinnamic acid is catalyzed by cimmamoyl-CoA ligase (CLL-7), chalcone synthase (CHS-2), chalcone isomerase (CHI) to form pinocembrin. Pinocembrin is then converted by a specialized isoform of flavone synthase (FNSII-2) to form chrysin, which could be further hydroxylated by flavone 6-hydroxylase (F6H) and flavone 8-hydroxylase (F8H) to produce baicalein and wogonin, respectively (Zhao et al. 2016a, 2016b, 2018). O-methyltransferases (OMTs) may participate in the biosynthesis of wogonin, though no OMT has been reported yet. Among the biosynthetic enzymes, SbCLL-7, SbCHS-2, FNSII-2 and F8H are expressed preferentially in the roots. Functions of these genes have been validated by RNAi in hairy roots of S. baicalensis and overexpression in transgenic Arabidopsis.
Binding site comparisons for target-centered drug discovery
Published in Expert Opinion on Drug Discovery, 2019
Binding site comparison has been used successfully as a stand-alone method [59,60] or in combination with inverse virtual screening [61] to identify new flavonoid targets. Following the hypothesis that flavonoids leave biological imprints in the active sites of the biosynthetic enzymes, in which they are synthesized, a method was proposed to detect these imprints in the binding sites of potential target proteins [59]. Active sites of five representative flavonoid biosynthetic enzymes were compared with 8,077 druggable binding sites from the PDB. The flavonoid biosynthetic enzymes were chalcone isomerase (CHI) and chalcone synthase (CHS), from a flowering plant Medicago sativa, quercetin 2,3-dioxygenase (2,3QD) from the Aspergillus japonicus fungus, and dihydroflavonol-4-reductase (DFR) and leucoanthocyanidin reductase 1 (LAR) from the Vitis vinifera canola grape. These enzymes act on nine different substrates in five different metabolic pathways of flavonoid metabolism, and thus were assumed to represent the possible modes of flavonoid recognition. The screening achieved a significant enrichment of already known flavonoid targets with the Area Under the ROC Curve ranging between 0.68 and 0.78 depending on the biosynthetic enzyme that was used as the query. The flavonoid biological imprint, which was incorporated in the CHI enzyme, produced the most relevant hits. The CHI list contained many known flavonoid targets, including human RAC-α serine/threonine protein kinase [62], human mitogen-activated protein kinase 1 [63] and human phosphatidylinositol 4,5-biphosphate 3-kinase catalytic subunit γ isoform [64], as well as many serine/threonine protein kinases. The diversity of flavonoid targets obtained using various flavonoid biosynthetic enzymes as queries indicated that the biological imprint obtained during the flavonoid biosynthesis is unique to each biosynthetic enzyme. It was suggested that it will be possible in the future to detect unknown targets of natural products that could then be biologically evaluated.