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Ikuro Abe - One of the best experts on this subject based on the ideXlab platform.

  • A structure-based mechanism for benzalacetone synthase from Rheum Palmatum
    Proceedings of the National Academy of Sciences of the United States of America, 2009
    Co-Authors: Hiroyuki Morita, Toshiyuki Kohno, Hiroshi Noguchi, Yoshihiko Shimokawa, Michikazu Tanio, Ryohei Kato, Shigetoshi Sugio, Ikuro Abe
    Abstract:

    Benzalacetone synthase (BAS), a plant-specific type III polyketide synthase (PKS), catalyzes a one-step decarboxylative condensation of malonyl-CoA and 4-coumaroyl-CoA to produce the diketide benzalacetone. We solved the crystal structures of both the wild-type and chalcone-producing I207L/L208F mutant of Rheum Palmatum BAS at 1.8 A resolution. In addition, we solved the crystal structure of the wild-type enzyme, in which a monoketide coumarate intermediate is covalently bound to the catalytic cysteine residue, at 1.6 A resolution. This is the first direct evidence that type III PKS utilizes the cysteine as the nucleophile and as the attachment site for the polyketide intermediate. The crystal structures revealed that BAS utilizes an alternative, novel active-site pocket for locking the aromatic moiety of the coumarate, instead of the chalcone synthase's coumaroyl-binding pocket, which is lost in the active-site of the wild-type enzyme and restored in the I207L/L208F mutant. Furthermore, the crystal structures indicated the presence of a putative nucleophilic water molecule which forms hydrogen bond networks with the Cys-His-Asn catalytic triad. This suggested that BAS employs novel catalytic machinery for the thioester bond cleavage of the enzyme-bound diketide intermediate and the final decarboxylation reaction to produce benzalacetone. These findings provided a structural basis for the functional diversity of the type III PKS enzymes.

  • Structure function analysis of benzalacetone synthase from Rheum Palmatum.
    Bioorganic & medicinal chemistry letters, 2007
    Co-Authors: Tsuyoshi Abe, Hiroyuki Morita, Hisashi Noma, Toshiyuki Kohno, Hiroshi Noguchi, Ikuro Abe
    Abstract:

    Benzalacetone synthase (BAS) is a plant-specific chalcone synthase (CHS) superfamily type III polyketide synthase (PKS) that catalyzes a one-step decarboxylative condensation of 4-coumaroyl-CoA with malonyl-CoA. The diketide forming activity of Rheum Palmatum BAS is attributed to the characteristic substitution of the conserved active-site Phe215 with Leu (numbering in Medicago sativa CHS). To further understand the structure and function of R. Palmatum BAS, four site-directed mutants (C197T, C197G, G256L, and S338V) were newly constructed. All the mutants did not change the product pattern, however, the activity was 2-fold increased in S338V, while reduced to half in G256L mutant. On the other hand, the C197 mutants were functionally almost identical to wild-type BAS, excluding the possibility that the second active-site Cys is involved in the enzyme reaction. Instead, homology modeling suggested a possibility that, unlike the case of CHS, BAS utilizes an alternative pocket to lock the coumaroyl moiety for the diketide formation reaction.

  • Chalcone synthase superfamily of type III polyketide synthases from rhubarb (Rheum Palmatum)
    Proceedings of the Japan Academy Series B, 2005
    Co-Authors: Ikuro Abe, Tatsuya Watanabe, Hiroshi Noguchi
    Abstract:

    Chalcone synthase (CHS), the pivotal enzyme in the biosynthesis of flavonoids, is a plant-specific type III polyketide synthase (PKS) that catalyzes a sequential condensation of 4-coumaroyl-CoA with three molecules of malonyl-CoA to produce naringenin chalcone. Two novel CHSs were for the first time cloned and sequenced from rhubarb (Rheum Palmatum), a medicinal plant rich in aromatic polyketides. Recombinant CHS1 and CHS2, sharing 90% amino acid sequence identity, showed KM = 61.1 M, kcat = 1.12 min-1, and KM = 36.1 M, kcat = 0.79 min-1 for 4-coumaroyl-CoA, respectively. Interestingly, CHS's conserved Thr197, the residue lining the active-site cavity, is uniquely replaced with Cys in CHS1 and CHS2. It was remarkable that both enzymes accepted long-chain fatty acyl CoAs up to the C20 chain length as a starter substrate to efficiently produce triketide and tetraketide α-pyrones. (Communicated by Shoji SHIBATA, M.J.A.)

Hiromu Kameoka - One of the best experts on this subject based on the ideXlab platform.

  • Volatile components of the Rhizomes of Rheum Palmatum L.
    Flavour and Fragrance Journal, 1996
    Co-Authors: Mitsuo Miyazawa, Yukiko Minamino, Hiromu Kameoka
    Abstract:

    The composition of the volatile oil from the rhizomes of Rheum Palmatum L. has been investigated by capillary GC, GC-MS and 1 H-NMR. The oil contained 108 volatile components of which 27.3% were terpenoid. The main constituents were palmitic acid (22.5%), paeonol (16.2%), α-copaene (9.8%), methyl stearate (9.3%), 8-cadinene (5.7%) and methyl eugenol (5.4%).

Bao Guo-rong - One of the best experts on this subject based on the ideXlab platform.

  • ESR Study on the scavenging effects of the free anthraquinones from Rheum Palmatum L. on superoxide anion radical
    Strait Pharmaceutical Journal, 2009
    Co-Authors: Bao Guo-rong
    Abstract:

    OBJECTIVE To study the scavenging effects of Rhein,Aloe-emodin,Emodin,Physcion and Chrysophanol which were the free anthraquinones from Rheum Palmatum L.on superoxide anion radical and to inverstigate the mechanism of Rheum Palmatum L.in retarding aging at molecular biology level.METHODS The electron spin resonance (ESR) was used to observe the scavenging effects on the superoxide anion radical (O·2) of the free anthraquinones from Rheum Palmatum L.RESULTS All of the Rhein,Aloe-emodin,Emodin,Physcion and Chrysophanol were effective inscavenging O·2 produced in the alkaline DMSO system,and the ability was RheinChrysophanolEmodinPhyscionAloe-emodin.CONCLUSION Rheum Palmatum L.has the effect of retarding aging.Perhaps this is relevant to the scavenging effects on the superoxide anion radical (O·2) of the free anthraquinones from the herb.

  • ESR Study on the Scavenging Effects of the Main Ingredients in Rheum Palmatum L. on Superoxide Anion Radical
    Chinese Archives of Traditional Chinese Medicine, 2007
    Co-Authors: Bao Guo-rong
    Abstract:

    Objective:To study the scavenging effects of Rhein,Aloe-emodin,Emodin,Physcion and Chrysophanol which were the main ingredients in Rheum Palmatum L.on superoxide anion radical and to investigate the mechanism of Rheum Palmatum L.in retarding aging at molecular biology lever.Methods: The electron spin resonance(ESR)was used to observe the scavenging effect on the superoxide anion radical(O2.-)of the main ingredients in Rheum Palmatum L.Results: All of the Rhein,Aloe-emodin,Emodin,Physcion and Chrysophanol were effective in scavenging O2.-produced in the alkaline DMSO system,and the ability was RheinChrysophanol EmodinPhyscionAloe-emodin.Conclusion:Rheum Palmatum L.has the effect of retarding aging.Perhaps this is relevant to the scavenging effects on the superoxide anion radical(O2.-)of the main ingredients in the herb.

Hiroshi Noguchi - One of the best experts on this subject based on the ideXlab platform.

  • A structure-based mechanism for benzalacetone synthase from Rheum Palmatum
    Proceedings of the National Academy of Sciences of the United States of America, 2009
    Co-Authors: Hiroyuki Morita, Toshiyuki Kohno, Hiroshi Noguchi, Yoshihiko Shimokawa, Michikazu Tanio, Ryohei Kato, Shigetoshi Sugio, Ikuro Abe
    Abstract:

    Benzalacetone synthase (BAS), a plant-specific type III polyketide synthase (PKS), catalyzes a one-step decarboxylative condensation of malonyl-CoA and 4-coumaroyl-CoA to produce the diketide benzalacetone. We solved the crystal structures of both the wild-type and chalcone-producing I207L/L208F mutant of Rheum Palmatum BAS at 1.8 A resolution. In addition, we solved the crystal structure of the wild-type enzyme, in which a monoketide coumarate intermediate is covalently bound to the catalytic cysteine residue, at 1.6 A resolution. This is the first direct evidence that type III PKS utilizes the cysteine as the nucleophile and as the attachment site for the polyketide intermediate. The crystal structures revealed that BAS utilizes an alternative, novel active-site pocket for locking the aromatic moiety of the coumarate, instead of the chalcone synthase's coumaroyl-binding pocket, which is lost in the active-site of the wild-type enzyme and restored in the I207L/L208F mutant. Furthermore, the crystal structures indicated the presence of a putative nucleophilic water molecule which forms hydrogen bond networks with the Cys-His-Asn catalytic triad. This suggested that BAS employs novel catalytic machinery for the thioester bond cleavage of the enzyme-bound diketide intermediate and the final decarboxylation reaction to produce benzalacetone. These findings provided a structural basis for the functional diversity of the type III PKS enzymes.

  • Structure function analysis of benzalacetone synthase from Rheum Palmatum.
    Bioorganic & medicinal chemistry letters, 2007
    Co-Authors: Tsuyoshi Abe, Hiroyuki Morita, Hisashi Noma, Toshiyuki Kohno, Hiroshi Noguchi, Ikuro Abe
    Abstract:

    Benzalacetone synthase (BAS) is a plant-specific chalcone synthase (CHS) superfamily type III polyketide synthase (PKS) that catalyzes a one-step decarboxylative condensation of 4-coumaroyl-CoA with malonyl-CoA. The diketide forming activity of Rheum Palmatum BAS is attributed to the characteristic substitution of the conserved active-site Phe215 with Leu (numbering in Medicago sativa CHS). To further understand the structure and function of R. Palmatum BAS, four site-directed mutants (C197T, C197G, G256L, and S338V) were newly constructed. All the mutants did not change the product pattern, however, the activity was 2-fold increased in S338V, while reduced to half in G256L mutant. On the other hand, the C197 mutants were functionally almost identical to wild-type BAS, excluding the possibility that the second active-site Cys is involved in the enzyme reaction. Instead, homology modeling suggested a possibility that, unlike the case of CHS, BAS utilizes an alternative pocket to lock the coumaroyl moiety for the diketide formation reaction.

  • Chalcone synthase superfamily of type III polyketide synthases from rhubarb (Rheum Palmatum)
    Proceedings of the Japan Academy Series B, 2005
    Co-Authors: Ikuro Abe, Tatsuya Watanabe, Hiroshi Noguchi
    Abstract:

    Chalcone synthase (CHS), the pivotal enzyme in the biosynthesis of flavonoids, is a plant-specific type III polyketide synthase (PKS) that catalyzes a sequential condensation of 4-coumaroyl-CoA with three molecules of malonyl-CoA to produce naringenin chalcone. Two novel CHSs were for the first time cloned and sequenced from rhubarb (Rheum Palmatum), a medicinal plant rich in aromatic polyketides. Recombinant CHS1 and CHS2, sharing 90% amino acid sequence identity, showed KM = 61.1 M, kcat = 1.12 min-1, and KM = 36.1 M, kcat = 0.79 min-1 for 4-coumaroyl-CoA, respectively. Interestingly, CHS's conserved Thr197, the residue lining the active-site cavity, is uniquely replaced with Cys in CHS1 and CHS2. It was remarkable that both enzymes accepted long-chain fatty acyl CoAs up to the C20 chain length as a starter substrate to efficiently produce triketide and tetraketide α-pyrones. (Communicated by Shoji SHIBATA, M.J.A.)

Jian Chen - One of the best experts on this subject based on the ideXlab platform.

  • Study on the Rheum Palmatum volatile oil against HBV in cell culture in vitro
    Zhong yao cai = Zhongyaocai = Journal of Chinese medicinal materials, 1998
    Co-Authors: Zhang B, Jian Chen
    Abstract:

    The antiHBV effect of Rheum Palmatum Volatile oil was studied by using 2215 cell line transfected with HBV DNA. At the same time MTT method was applied for the detection of cytoxicity of drugs, selecting acyclovir(ACV) as control medicine. It turns out that the toxic concentration of Rheum Palmatum Volatile oil for 50% cells was (CD50) > 1.25 x 10(-1) g/L. When concentration was below 0.625 x 10(-1) g/L, the survival rate of cells was over 90%. The maximum inhibitory rates for HBsAg and HBeAg were 70.71 +/- 5.4% and 30.99 +/- 5.3% respectively. This shows Rheum Palmatum Volatile oil possesses the effect of antiHBV in vitro.

  • Effects of volatile oil from Rheum Palmatum on immunologic function in mice
    Zhong yao cai = Zhongyaocai = Journal of Chinese medicinal materials, 1997
    Co-Authors: Zhang B, Jian Chen, Chen H, Sheng S
    Abstract:

    The effects of volatile oil from Rheum Palmatum (RVO) on immunologic function in mice are studied. The results show that the delayed type hypersensitivity (DTH) induced by 2, 4-dinitrochlorobenzene, lymphocytes transformation of (3H)-TdR induced by PHA, clearance rate of ivcarbon particles, phagocytic function of peritioneal macrophage and production of hemolysin induced by SRBC are markeyly increased with RVO given by oral administration or inhalation.