Masumi Ishizaka

Publications of Masumi Ishizaka

• Host plant genome overcomes the lack of a bacterial gene for symbiotic nitrogen fixation.

  Authors: Tsuneo Hakoyama, Kaori Niimi, Hirokazu Watanabe, Ryohei Tabata, Junichi Matsubara, Shusei Sato, Yasukazu Nakamura, Satoshi Tabata, Li Jichun, Tsuyoshi Matsumoto, Kazuyuki Tatsumi, Mika Nomura, Shigeyuki Tajima, Masumi Ishizaka, Koji Yano, Haruko Imaizumi-Anraku, Masayoshi Kawaguchi, Hiroshi Kouchi, Norio Suganuma

  Nature. 11/2009; 462(7272):514-7.

  Homocitrate is a component of the iron-molybdenum cofactor in nitrogenase, where nitrogen fixation occurs. NifV, which encodes homocitrate synthase (HCS), has been identified from various diazotrophsHomocitrate is a component of the iron-molybdenum cofactor in nitrogenase, where nitrogen fixation occurs. NifV, which encodes homocitrate synthase (HCS), has been identified from various diazotrophs but is not present in most rhizobial species that perform efficient nitrogen fixation only in symbiotic association with legumes. Here we show that the FEN1 gene of a model legume, Lotus japonicus, overcomes the lack of NifV in rhizobia for symbiotic nitrogen fixation. A Fix(-) (non-fixing) plant mutant, fen1, forms morphologically normal but ineffective nodules. The causal gene, FEN1, was shown to encode HCS by its ability to complement a HCS-defective mutant of Saccharomyces cerevisiae. Homocitrate was present abundantly in wild-type nodules but was absent from ineffective fen1 nodules. Inoculation with Mesorhizobium loti carrying FEN1 or Azotobacter vinelandii NifV rescued the defect in nitrogen-fixing activity of the fen1 nodules. Exogenous supply of homocitrate also recovered the nitrogen-fixing activity of the fen1 nodules through de novo nitrogenase synthesis in the rhizobial bacteroids. These results indicate that homocitrate derived from the host plant cells is essential for the efficient and continuing synthesis of the nitrogenase system in endosymbionts, and thus provide a molecular basis for the complementary and indispensable partnership between legumes and rhizobia in symbiotic nitrogen fixation.

• Arsenic Speciation in Rice and Soil Containing Related Compounds of Chemical Warfare Agents.

  Authors: Koji Baba, Tomohito Arao, Yuji Maejima, Eiki Watanabe, Heesoo Eun, Masumi Ishizaka

  Analytical chemistry. 07/2008;

  Diphenylarsinic acid, phenylarsonic acid, methylphenylarsinic acid (MPAA), dimethylphenylarsine oxide (DMPAO), and methyldiphenylarsine oxide (MDPAO) in soil and rice were extracted, separated byDiphenylarsinic acid, phenylarsonic acid, methylphenylarsinic acid (MPAA), dimethylphenylarsine oxide (DMPAO), and methyldiphenylarsine oxide (MDPAO) in soil and rice were extracted, separated by reversed-phase chromatography, and quantified by ICPMS with a membrane desolvating system. For the extraction of arsenicals from rice grain and straw, 68% HNO 3 provided better extraction efficiency than water, 50% methanol, or 2.0 mol L (-1) trifluoroacetic acid. For the extraction from soil, 68% HNO 3 provided better extraction efficiency than H 2O, 1 mol L (-1) H 3PO 4, or 1 mol L (-1) NaOH. The contaminated soil contained all five aromatic arsenicals along with inorganic arsenicals as main species (5.86 +/- 0.19 mug of As kg (-1): 60.8 +/- 2.0% of total extracted As). After pot experiments, rice straw contained mainly DMPAO (7.71 +/- 0.48 mug of As kg (-1): 60.5 +/- 3.7%), MDPAO (0.91 +/- 0.07 mug of As kg (-1): 7.2 +/- 0.5%), and inorganic As (2.85 +/- 0.20 mug of As kg (-1): 22.3 +/- 1.6%). On the other hand, rice grain contained mainly MPAA (1.17 +/- 0.04 mug of As kg (-1): 86.7 +/- 2.7%). The root uptake of each species from the soil and transport from straw to grains were significantly related to the calculated log K ow values.

• Monitoring of cholinesterase-inhibiting activity in water from the Tone canal, Japan, as a biomarker of ecotoxicity.

  Authors: Tsuyoshi Kawakami, Aya Takezawa, Iwaki Nishi, Eiki Watanabe, Masumi Ishizaka, Heesoo Eun, Sukeo Onodera

  Ecotoxicology (London, England). 06/2008; 17(4):221-8.

  The cholinesterase (ChE)-inhibiting activity of water and the concentrations of representative inhibitors were monitored in the Tone canal, Japan, during April to December 2006. The ChE-inhibitingThe cholinesterase (ChE)-inhibiting activity of water and the concentrations of representative inhibitors were monitored in the Tone canal, Japan, during April to December 2006. The ChE-inhibiting activity, measured by using horse serum as enzyme source, increased from late April to early June, and from September to October. Although the trends in the ChE-inhibiting activity of the samples were consistent with concentration changes of organophosphorus pesticides, ChE-inhibiting activity was not observed in samples replicated on the basis of the chemical concentrations detected. The water samples were treated with chlorine to enhance the ChE-inhibiting activity by conversion of thiophosphate pesticides to phosphate pesticides. The ChE-inhibiting activity increased in almost all the chlorine-treated samples, although organophosphorus pesticides were either not detected or detected in traces in the samples by gas chromatographic-mass spectrometric analysis. These results suggested that assay of ChE-inhibiting activity is important for evaluating the ecotoxicity of environmental water, because toxicological investigations based solely on inhibitor concentrations may underestimate the contamination. Furthermore, the combined method of oxidation by chlorination and the ChE assay is very effective for screening and monitoring of organophosphorus pesticides in environmental water.

• Glucose-sulfate conjugates as a new phase II metabolite formed by aquatic crustaceans.

  Authors: Yoshinori Ikenaka, Masumi Ishizaka, Heesoo Eun, Yuichi Miyabara

  Biochemical and biophysical research communications. 09/2007; 360(2):490-5.

  We found that aquatic crustaceans, decapoda; atyidae (Caridina multidentata, Neocaridina denticulate, and Paratya compressa), metabolize pyrene to a new conjugation product. The results ofWe found that aquatic crustaceans, decapoda; atyidae (Caridina multidentata, Neocaridina denticulate, and Paratya compressa), metabolize pyrene to a new conjugation product. The results of deconjugation treatments indicated that glucose and sulfate combined with 1-hydroxypyrene. Further analysis by LC/ESI-MS/MS showed that the molecular weight of the product was 460 (m/z 459; deprotonated ion), and that it has a glucose-sulfate moiety (m/z 241; fragment ion). These results indicated that the new metabolite was the glucose-sulfate conjugate of 1-hydroxypyrene. The glucose-sulfate conjugate is a phase II product that has not been reported previously from any organism. Several studies have demonstrated that sulfation is an important pathway for metabolism of xenobiotics in aquatic invertebrates. Thus, glucose-sulfate conjugates may add an important signal for excretion or sequestration of xenobiotics for aquatic invertebrates.

• Adsorption and desorption characteristics of several herbicides on sediment.

  Authors: Tsuyoshi Kawakami, Heesoo Eun, Masumi Ishizaka, Shozo Endo, Kenji Tamura, Teruo Higashi

  Journal of environmental science and health. Part. B, Pesticides, food contaminants, and agricultural wastes. 02/2007; 42(1):1-8.

  The objective of this study was to clarify the adsorption and desorption characteristics of several herbicides in sediment. Five herbicides, esprocarb, thiobencarb, dimethametryn, pretilachlor, andThe objective of this study was to clarify the adsorption and desorption characteristics of several herbicides in sediment. Five herbicides, esprocarb, thiobencarb, dimethametryn, pretilachlor, and simetryn were examined in this study. The adsorption ratio on the sediment increased in the following order: pretilachlor < dimethametryn < simetryn < thiobencarb < esprocarb. On the other hand, the adsorption ratio on the sediment without organic matter increased in the following order: thiobencarb < esprocarb < pretilachlor < dimethametryn < simetryn. Furthermore, the amounts of simetryn, dimethametryn, and pretilachlor adsorbed on the sediment without organic matter increased, while those of esprocarb and thiobencarb decreased in comparison to the original sediment. These results strongly suggested that the mineral surface in the sediment was very important as the adsorption site for the herbicide, especially in the case of simetryn, dimethametryn, and pretilachlor. All the adsorption and desorption data fitted well with the Freundlich equation. The hysteresis in the adsorption-desorption phenomena in the sediment was observed for all the herbicides, and it was affected by the organic matter in sediment, especially in the case of dimethametryn and pretilachlor.

• Metabolism of pyrene by aquatic crustacean, Daphnia magna.

  Authors: Yoshinori Ikenaka, Heesoo Eun, Masumi Ishizaka, Yuichi Miyabara

  Aquatic toxicology (Amsterdam, Netherlands). 12/2006; 80(2):158-65.

  The aquatic crustacean Daphnia magna is an important species for ecotoxicological study, and is often used as a test organism for environmental risk assessment. However, the mechanism of xenobioticThe aquatic crustacean Daphnia magna is an important species for ecotoxicological study, and is often used as a test organism for environmental risk assessment. However, the mechanism of xenobiotic metabolism by this species has not been studied in detail. In the present study, pyrene was used as model substance to investigate the mechanism of xenobiotic metabolism in D. magna. The results of 24-h exposure experiments showed that D. magna could metabolize pyrene and biotransform it into water-soluble metabolites. On the other hand, the metabolism of pyrene was significantly inhibited by SKF-525A as the cytochrome P450 (CYP) inhibitor. These observations indicated that oxidation by CYP participated in the biotransformation of pyrene by D. magna. We also identified the pyrene metabolites formed by D. magna by HPLC with an electrospray ionization triple quadrupole mass spectrometry detector (LC/ESIMS/MS) and de-conjugation by sulfatase, beta-glucuronidase, and beta-glucosidase. One of the metabolites was ionized in ESI negative mode and formed a dominant mass of m/z 297 (MS) with the product ion of m/z 217 (MS2). Furthermore, this metabolite formed 1-hydroxypyrene on treatment with sulfatase. This metabolite was considered to be a sulfate conjugate of oxidized pyrene (1-hydroxypyrenesulfate). Furthermore, we quantified the deconjugated 1-hydroxypyrene formed by the above enzyme treatment. It showed that 52% of the total metabolized pyrene was biotransformed into 1-hydroxypyrene-sulfate, and more than 73% was biotransformed into oxidized pyrene conjugate. These results indicated that CYP and several conjugation enzymes participate in its biotransformation, and sulfation is important in D. magna for metabolism and elimination of xenobiotics.

• Reliable enzyme immunoassay detection for chlorothalonil: fundamental evaluation for residue analysis and validation with gas chromatography.

  Authors: Eiki Watanabe, Shiro Miyake, Shigekazu Ito, Koji Baba, Heesoo Eun, Masumi Ishizaka, Shozo Endo

  Journal of chromatography. A. 10/2006; 1129(2):273-82.

  This work describes the analytical performance of the enzyme-linked immunosorbent assay (ELISA) for the fungicide chlorothalonil to effectively exploit as a simple and rapid detection system forThis work describes the analytical performance of the enzyme-linked immunosorbent assay (ELISA) for the fungicide chlorothalonil to effectively exploit as a simple and rapid detection system for pesticide residue on the scenes of the agricultural production and distribution. This ELISA represents the satisfactory analytical characteristics (I50 value, 0.34 ng/g; limit of detection, 0.052 ng/g) to detect chlorothalonil at the regulatory values or thereabout in a sample. Noticeable cross-reactivities were shown with two fungicides, fthalide (58.8%) and pentachloronitrobenzene (quintozene) (20.0%), and some non-agrochemicals such as tetrachloroterephthalonitrile (96.8%) and tetrachlorophthalonitrile (68.3%). The influence of three organic solvents (methanol, acetone, and acetonitrile) used as extractants for chlorothalonil residue was evaluated, with the result that methanol was the most suitable solvent for the ELISA, and the final concentration in the well could be up to 5% (v/v) without any negative influence on the ELISA. It has been possible to directly analyze chlorothalonil residue only by giving dilution of each sample extract with water prior to the ELISA analysis. The average recovery values from the spiked samples by the ELISA were between 101.7 and 113.6% with the average coefficients of variation between 2.6 and 5.9%. Although the results obtained from the ELISA correlated well with those from the reference GC/MS methods for all agricultural samples (r>0.98), the linear function inclined to the ELISA results because of loss during complex sample preparations for GC/MS analysis. Nevertheless, the results demonstrated that the proposed ELISA is a reliable, cost-effective, and rapid quantitative method for chlorothalonil residue.

• Lolitrem B residue in fat tissues of cattle consuming endophyte-infected perennial ryegrass straw.

  Authors: Shigeru Miyazaki, Ikumi Ishizaki, Masumi Ishizaka, Tadashi Kanbara, Yuriko Ishiguro-Takeda

  Journal of veterinary diagnostic investigation : official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc. 08/2004; 16(4):340-2.

  Lolitrems are neurotoxins found in endophyte-infected perennial ryegrass. Lolitrems, primarily lolitrem B, are the causative agents of ryegrass staggers in livestock. To guarantee the safety of meatLolitrems are neurotoxins found in endophyte-infected perennial ryegrass. Lolitrems, primarily lolitrem B, are the causative agents of ryegrass staggers in livestock. To guarantee the safety of meat produced from cattle consuming endophyte-infected perennial ryegrass, lolitrem B concentrations in tissues of Japanese Black cattle were determined using high-performance liquid chromatography. Lolitrem B was not detected in muscle, liver, kidney, or cerebrum of a Japanese Black cow with signs of ryegrass staggers. In contrast, perirenal fat contained 210 ppb lolitrem B. Three cows that received half as much perennial ryegrass straw as the cow with ryegrass staggers showed no clinical signs of ryegrass staggers. However, low concentrations of lolitrem B (less than 150 ppb) were detected in their fat tissue. These observations indicate that human exposure to the neurotoxic effect of lolitrem B through beef is unlikely. The amount of lolitrem B consumed by cattle can be estimated by the determination of lolitrem B in fat tissue.

• Isolation and characterization of a rice dwarf mutant with a defect in brassinosteroid biosynthesis.

  Authors: Masaki Mori, Takahito Nomura, Hisako Ooka, Masumi Ishizaka, Takao Yokota, Kazuhiko Sugimoto, Ken Okabe, Hideyuki Kajiwara, Kouji Satoh, Koji Yamamoto, Hirohiko Hirochika, Shoshi Kikuchi

  Plant physiology. 12/2002; 130(3):1152-61.

  We have isolated a new recessive dwarf mutant of rice (Oryza sativa L. cv Nipponbare). Under normal growth conditions, the mutant has very short leaf sheaths; has short, curled, and frizzled leafWe have isolated a new recessive dwarf mutant of rice (Oryza sativa L. cv Nipponbare). Under normal growth conditions, the mutant has very short leaf sheaths; has short, curled, and frizzled leaf blades; has few tillers; and is sterile. Longitudinal sections of the leaf sheaths revealed that the cell length along the longitudinal axis is reduced, which explains the short leaf sheaths. Transverse sections of the leaf blades revealed enlargement of the motor cells along the dorsal-ventral axis, which explains the curled and frizzled leaf blades. In addition, the number of crown roots was smaller and the growth of branch roots was weaker than those in the wild-type plant. Because exogenously supplied brassinolide considerably restored the normal phenotypes, we designated the mutant brassinosteroid-dependent 1 (brd1). Further, under darkness, brd1 showed constitutive photomorphogenesis. Quantitative analyses of endogenous sterols and brassinosteroids (BRs) indicated that BR-6-oxidase, a BR biosynthesis enzyme, would be defective. In fact, a 0.2-kb deletion was detected in the genomic region of OsBR6ox (a rice BR-6-oxidase gene) in the brd1 mutant. These results indicate that BRs are involved in many morphological and physiological processes in rice, including the elongation and unrolling of leaves, development of tillers, skotomorphogenesis, root differentiation, and reproductive growth, and that the defect of BR-6-oxidase caused the brd1 phenotype.

• Reliable enzyme immunoassay detection for chlorothalonil: Fundamental evaluation for residue analysis and validation with gas chromatography

  Authors: Eiki Watanabe, Shiro Miyake, Shigekazu Ito, Koji Baba, Heesoo Eun, Masumi Ishizaka, Shozo Endo

  Journal of Chromatography A.

  This work describes the analytical performance of the enzyme-linked immunosorbent assay (ELISA) for the fungicide chlorothalonil to effectively exploit as a simple and rapid detection system forThis work describes the analytical performance of the enzyme-linked immunosorbent assay (ELISA) for the fungicide chlorothalonil to effectively exploit as a simple and rapid detection system for pesticide residue on the scenes of the agricultural production and distribution. This ELISA represents the satisfactory analytical characteristics (I50 value, 0.34 ng/g; limit of detection, 0.052 ng/g) to detect chlorothalonil at the regulatory values or thereabout in a sample. Noticeable cross-reactivities were shown with two fungicides, fthalide (58.8%) and pentachloronitrobenzene (quintozene) (20.0%), and some non-agrochemicals such as tetrachloroterephthalonitrile (96.8%) and tetrachlorophthalonitrile (68.3%). The influence of three organic solvents (methanol, acetone, and acetonitrile) used as extractants for chlorothalonil residue was evaluated, with the result that methanol was the most suitable solvent for the ELISA, and the final concentration in the well could be up to 5% (v/v) without any negative influence on the ELISA. It has been possible to directly analyze chlorothalonil residue only by giving dilution of each sample extract with water prior to the ELISA analysis. The average recovery values from the spiked samples by the ELISA were between 101.7 and 113.6% with the average coefficients of variation between 2.6 and 5.9%. Although the results obtained from the ELISA correlated well with those from the reference GC/MS methods for all agricultural samples (r > 0.98), the linear function inclined to the ELISA results because of loss during complex sample preparations for GC/MS analysis. Nevertheless, the results demonstrated that the proposed ELISA is a reliable, cost-effective, and rapid quantitative method for chlorothalonil residue.