The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform

Hiroki Hamada - One of the best experts on this subject based on the ideXlab platform.

Kei Shimoda - One of the best experts on this subject based on the ideXlab platform.

Atsushi Komamine - One of the best experts on this subject based on the ideXlab platform.

  • Inhibition of Betacyanin Accumulation by Abscisic Acid in Suspension Cultures of Phytolacca Americana
    Zeitschrift für Naturforschung C, 1996
    Co-Authors: Hiroshi Hirano, Masaaki Sakuta, Atsushi Komamine
    Abstract:

    Growth of cells and the accumulation of betacyanin were suppressed by the addition of abscisic acid (ABA) to suspension cultures of Phytolacca Americana. The decrease in the accumulation of betacyanin was overcome by exogenously supplied tyrosine which is a precursor of betacyanin. ABA decreased the level of free tyrosine in the cells. Feeding experiments using labeled tyrosine revealed that ABA reduced the incorporation of labeled tyrosine into betacyanins (to about 50% of the control rate). These results suggest that both the availability of tyrosine and the biosynthetic activity of the pathway from tyrosine to the betacyanins are involved in the inhibition of the accumulation of betacyanins by ABA in Phytolacca Americana cells.

  • betacyanins from plants and cell cultures of Phytolacca Americana
    Phytochemistry, 1996
    Co-Authors: Willibald Schliemann, Atsushi Komamine, Jorg W Metzger, Manfred Nimtz, Victor Wray, Dieter Strack
    Abstract:

    Abstract Betacyanins from cell cultures of Phytolacca Americana were characterized and compared with those of the stems and ripening fruits of the plant. Whereas in fruits prebetanin (betanin 6′-O-sulphate) and its isoform predominate, in the stem and cell cultures feruloylated derivatives occur as the major components. These were rigorously identified by various spectroscopic techniques (DAD-HPLC, NMR, LC-MS and electrospray MS-MS) and carbohydrate analyses as betanidin 5-O-[(5″-O-E- feruloyl )-2′-O-β- d - apiofuranosyl ]-β- d - glucopyranoside , a new betacyanin of higher plants, and betanidin 5-O-(6′-O-E- feruloyl )-β- d - glucopyranoside (lampranthin II), together with their isoforms.

  • cloning and characterization of polyphenol oxidase cdnas of Phytolacca Americana
    Plant Physiology, 1995
    Co-Authors: Munetaka Sugiyama, Hiroo Fukuda, Atsushi Komamine
    Abstract:

    Two cDNA clones encoding polyphenol oxidases were isolated from a cDNA library constructed from a log-phase suspension culture of Phytolacca Americana (pokeweed) producing betalains. The clones exhibit 93 and 86% sequence identity at the nucleotide and deduced amino acid levels, respectively. Both clones contain two copper-binding domains characterized by histidine-rich regions, which are found ubiquitously in all polyphenol oxidases/tyrosinases, and a putative third histidine-rich, copper-binding region, which is common to all plant polyphenol oxidases. One of the Phytolacca cDNA deduced amino acid sequences contains the ubiquitous transit peptide for all proteins targeted to the internal lumen of thylakoid membranes of plastids and is considered to be 98 residues in length based on a proposed sequence cleavage site motif. This would produce a processed peptide of approximately 54 kD. In addition to common features of transit peptides, it was found that an additional conserved region for polyphenol oxidases was located between the hydroxy amino acid-rich region and the thylakoid transfer domain. Spatial and temporal expression was investigated by northern blot analysis of total RNA from various organs of Phytolacca plants. Transcripts of the two clones were found to be 2.1 and 2.3 kb, respectively. Both transcripts were present only at substantial levels in ripening, betalain-containing fruit.

  • correlation of betacyanin synthesis with cell division in cell suspension cultures of Phytolacca Americana
    Physiologia Plantarum, 1994
    Co-Authors: Hiroshi Hirano, Atsushi Komamine
    Abstract:

    In suspension cultures of Phytolacca Americana, betacyanin accumulation was reduced when cell division was inhibited by treatment with various inhibitors of DNA synthesis or anti-microtubule drugs. Aphidicolin (APC), an inhibitor of DNA synthesis, reduced the incorporation of radioactivity from labeled tyrosine into betacyanin, but the incorporation of radioactivity from labeled 3,4-dihydroxyphenylalanine (DOPA) into betacyanin was not affected by similar treatments. Propyzamide, another anti-microtubule drug, reduced incorporation of radioactivity from tyrosine and DOPA into betacyanin. However, the rate of incorporation from DOPA was higher than that from tyrosine. The results suggest that inhibition of betacyanin accumulation in Phytolacca Americana cells by APC and propyzamide is due to suppression of the reaction converting tyrosine to DOPA, which may be closely related to cell division.

  • Inhibition by Cytokinin of the Accumulation of Betacyanin in Suspension Cultures of Phytolacca Americana
    Zeitschrift für Naturforschung C, 1992
    Co-Authors: Hiroshi Hirano, Masaaki Sakuta, Atsushi Komamine
    Abstract:

    The accumulation of betacyanin was reduced by the addition of various cytokinins to suspension cultures of Phytolacca Americana. The decrease in the accumulation of betacyanin was overcome by exogenously supplied tyrosine which is a precursor of betacyanin. Benzylaminopurine (BAP) decreased the level of free tyrosine in the cells. Feeding experiments using labeled tyrosine revealed that BAP reduced the incorporation of labeled tyrosine into betacyanins (to about 50% of the control rate). These results suggest that both the availability of tyrosine and the biosynthetic activity of the pathway from tyrosine to the betacyanins are involved in the inhibition of the accumulation of betacyanins by cytokinins in Phytolacca Americana cells.

Shinichi Ozaki - One of the best experts on this subject based on the ideXlab platform.

  • An ambidextrous polyphenol glycosyltransferase PaGT2 from Phytolacca Americana.
    Biochemistry, 2020
    Co-Authors: Rakesh Maharjan, Hiroki Hamada, Toru Nakayama, Yohta Fukuda, Naomichi Shimomura, Taisuke Nakayama, Yuta Okimoto, Koki Kawakami, Tsuyoshi Inoue, Shinichi Ozaki
    Abstract:

    Glycosylation of small hydrophobic compounds is catalyzed by uridine diphosphate glycosyltransferases (UGTs). Since glycosylation is an invaluable tool for improving stability and water solubility of hydrophobic compounds, UGTs have gained attention for their application in food, cosmetics, and pharmaceutical industries. However, the ability of UGTs to accept and glycosylate a wide range of substrates is not clearly understood due to the existence of a large number of UGTs. PaGT2, a UGT from Phytolacca Americana is able to regioselectively glycosylate piceatannol but has low activity towards other stilbenoids. In order to elucidate the substrate specificity and catalytic mechanism, we determined the crystal structures of PaGT2 with and without substrates and performed molecular docking studies. The structures have revealed key residues involved in substrate recognition and suggest the presence of a non-conserved catalytic residue (His81) in addition to the highly conserved catalytic histidine in UGTs (His18). The role of the identified residues in substrate recognition and catalysis is elucidated with the mutational assay. Additionally, the structure-guided mutation of Cys142 to other residues, Ala, Phe, and Gln, allows PaGT2 to glycosylate resveratrol with high regioselectivity, which is negligibly glycosylated by the wildtype enzyme. These results provide a basis for tailoring an efficient glycosyltransferase.

  • synthesis of glycosides of resveratrol pinostilbene and piceatannol by bioconversion with Phytolacca Americana
    Natural Product Communications, 2019
    Co-Authors: Kei Shimoda, Naoji Kubota, Daisuke Uesugi, Yuya Fujitaka, Hiroki Hamada, Atsuhito Kuboki, Yuya Kiriake, Takafumi Iwaki, Tomohiro Saikawa, Shinichi Ozaki
    Abstract:

    Cultured cells of Phytolacca Americana, which had been cultivated in the dark, biotransformed resveratrol to pinostilbene and pterostilbene 4′-O-β-d-glucoside, together with the 3- and 4′-O-β-D-glu...

  • Phytolacca Americana pagt2 is an ambidextrous polyphenol glucosyltransferase
    bioRxiv, 2019
    Co-Authors: Rakesh Maharjan, Hiroki Hamada, Toru Nakayama, Yohta Fukuda, Naomichi Shimomura, Taisuke Nakayama, Tsuyoshi Inoue, Shinichi Ozaki
    Abstract:

    The health benefits of polyphenols have attracted their use as potential therapeutic agents, food additives, and cosmetics. However, low water solubility of polyphenols limits their cell absorbability, obscuring further exploration. Glycosylation is known to enhance the solubility of polyphenols preserving their pharmacological properties. Here, we show that a uridine diphosphate (UDP) glucosyltransferase from Phytolacca Americana ( Pa GT2) regioselectively catalyzes the transfer of glucose from UDP-glucose to stilbenoids such as piceatannol and flavonoids such as kaempferol. To understand the structure-function relationship of Pa GT2, we determined the crystal structure of Pa GT2 as well as Pa GT2 complexed with donor analogue UDP-2-fluoro glucose and stilbenoid acceptor analogues. While only one conserved histidine residue is recognized as a catalytic residue in known UGTs, the crystal structures of Pa GT2 suggested the presence of two catalytically active residues (His18 and His81) at two sides of the catalytic pocket. Although the single catalytic residue mutant His18Ala or His81Ala did not completely impair the glucosylation activity of the enzyme, the double mutant His18Ala/His81Ala failed to form glucoside products. These results showed that both catalytic residues in Pa GT2 actively and independently catalyze glucosylation, hence we called PaGT2 as an ambidextrous UGT. The information from Pa GT2 will be advantageous for the engineering of efficient biocatalysts for production of therapeutic polyphenols.

  • glucosylation of hydroxyflavones by glucosyltransferases from Phytolacca Americana
    Journal of Molecular Catalysis B-enzymatic, 2013
    Co-Authors: Tomoya Iwakiri, Hiroki Hamada, Shogo Mase, Tomonori Murakami, Masahiro Matsumoto, Toru Nakayama, Shinichi Ozaki
    Abstract:

    Abstract Cell suspension cultures of Phytolacca Americana can glucosylate 6- and 7-hydroxyflavone, but not 5-hydroxyflavone. In order to identify the enzymes responsible for these transformations, glucosyltransferases (GTs) from P. Americana were overexpressed in Escherichia coli and purified. The purified Pa GT3 enzyme could glucosylate 6- and 7-hydroxyflavone when incubated with UDP-glucose, a glucosyl donor molecule, but Pa GT2 could conjugate a glucose moiety only to 6-hydroxyflavone. E. coli cells expressing Pa GT2 and 3 could also be utilized for the glucosylation of hydroxyflavones. The glucoside products which had accumulated in the medium of overnight E. coli cell cultures were isolated using hydrophobic resins. This methodology might be suitable for the glucosylation of aglycones with important health-related properties.

  • synthesis of 3 5 3 4 tetrahydroxy trans stilbene 4 o beta d glucopyranoside by glucosyltransferases from Phytolacca Americana
    Natural Product Communications, 2013
    Co-Authors: Tomoya Iwakiri, Hiroki Hamada, Toru Nakayama, Hiroya Imai, Shinichi Ozaki
    Abstract:

    : Two glucosyltransferase isozymes from Phytolacca Americana, PaGT3 and PaGT2, catalyzed stereo- and regio-selective monoglucosylation of 3,5,3',4'-tetrahydroxy-trans-stilbene to yield 3,5,3',4'-tetrahydroxy-trans-stilbene-4'-O-beta-D-glucopyranoside.

Hatsuyuki Hamada - One of the best experts on this subject based on the ideXlab platform.