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951.
Formononetin (7-hydroxy-4'-methoxyisoflavone, also known as 4'-O-methyldaidzein) is an essential intermediate of ecophysiologically active leguminous isoflavonoids. The biosynthetic pathway to produce 4'-methoxyl of formononetin has been unknown because the methyl transfer from S-adenosyl-L-methionine (SAM) to 4'-hydroxyl of daidzein has never been detected in any plants. A hypothesis that SAM: daidzein 7-O-methyltransferase (D7OMT), an enzyme with a different regiospecificity, is involved in formononetin biosynthesis through its intracellular compartmentation with other enzymes recently prevails, but no direct evidence has been presented. We proposed a new scheme of formononetin biosynthesis involving 2,7,4'-trihydroxyisoflavanone as the methyl acceptor and subsequent dehydration. We now cloned a cDNA encoding SAM: 2,7,4'-trihydroxyisoflavanone 4'-O-methyltransferase (HI4'OMT) through the screening of functionally expressed Glycyrrhiza echinata (Fabaceae) cDNAs. The reaction product, 2,7-dihydroxy-4'-methoxyisoflavanone, was unambiguously identified. Recombinant G. echinata D7OMT did not show HI4'OMT activity, and G. echinata HI4'OMT protein free from D7OMT was partially purified. HI4'OMT is thus concluded to be distinct from D7OMT, and their distant phylogenetic relationship was further presented. HI4'OMT may be functionally identical to (+)-6a-hydroxymaackiain 3-OMT of pea. Homologous cDNAs were found in several legumes, and the catalytic function of the Lotus japonicus HI4'OMT was verified, indicating that HI4'OMT is the enzyme of formononetin biosynthesis in general legumes. 相似文献
952.
953.
954.
Summary. The aim of this work was to study the activity of NAD(P)H:(quinone acceptor) oxidoreductase 1 (EC 1.6.99.2) in the regeneration
of lipophilic antioxidants, alpha-tocopherol, and reduced-coenzyme Q analogs. First, we tested whether or not two isoforms
of the NAD(P)H:(quinone acceptor) oxidoreductase 1 designated as “hydrophilic” and “hydrophobic” (H. J. Prochaska and P. Talalay,
Journal of Biological Chemistry 261: 1372–1378, 1986) show differential enzyme activities towards hydrophilic or hydrophobic
ubiquinone homologs. By chromatography on phenyl Sepharose, we purified the two isoforms from pig liver cytosol and measured
their reduction of several ubiquinone homologs of different side chain length. We also studied by electron paramagnetic resonance
the effect of NAD(P)H:(quinone acceptor) oxidoreductase 1 on steady-state levels of chromanoxyl radicals generated by linoleic
acid and lipooxygenase and confirmed the enzyme's ability to protect alpha-tocopherol against oxidation induced with H2O2-Fe2+. Our results demonstrated that the different hydrophobicities of the isoforms do not reflect different reactivities towards
ubiquinones of different side chain length. In addition, electron paramagnetic resonance studies showed that in systems containing
the reductase plus NADH, levels of chromanoxyl radicals were dramatically reduced. Morever, in the presence of oxidants, alpha-tocopherol
was preserved by NAD(P)H:(quinone acceptor) oxidoreductase 1, supporting our hypothesis that regeneration of alpha-tocopherol
may be one of the physiologic functions of this enzyme.
Received May 20, 2002; accepted September 20, 2002; published online May 21, 2003
RID="*"
ID="*" Correspondence and reprints: Departamento de Biología Celular, Fisiología e Inmunología, Facultad de Ciencias, Edificio
Severo Ochoa, Campus de Rabanales, Universidad de Córdoba, 14014 Córdoba, Spain. 相似文献
955.
956.
Brito CA Silva LM Jucá N Leal NC de Souza W Queiroz D Cordeiro F Silva NL 《Memórias do Instituto Oswaldo Cruz》2003,98(6):817-821
Geographical differences in the prevalence of Helicobacter pylori genes and their association with disease severity have been identified. This study analyzes the prevalences of the cagA gene and alleles of the vacA gene in H. pylori-associated gastroduodenal diseases in isolates from Recife, PE, Brazil. Gastric biopsy of 61 H. pylori-positive patients were submitted to DNA extraction and gene amplification by polymerase chain reaction. Among the 61 patients, 21 suffered from duodenal ulcer (DU) and 40 from gastritis (GT). The prevalence of H. pylori strains harbouring the cagA gene was higher in the DU group (90.5%) than in the GT group (60%) (p=0.02). The vacA gene was amplified in 56 out of 61 biopsies, of which 43 (76.8%) contained bacteria carrying the s1 allele and 13 (23.2%) the s2. However, the prevalence of the vacA s1 genotyping was the same in either DU or GT group. The majority of the s1-typed strains, 39 (90.7%) out of 43, were subtype s1b. In resume there was a strong association between the H. pylori cagA+ gene and DU. However, there were no differences between the DU and GT groups in relation to the vacA s1 and s2 alleles distribution, albeit the subtype s1b was predominant. 相似文献
957.
Species-specific exclusion of APOBEC3G from HIV-1 virions by Vif 总被引:35,自引:0,他引:35
Mariani R Chen D Schröfelbauer B Navarro F König R Bollman B Münk C Nymark-McMahon H Landau NR 《Cell》2003,114(1):21-31
958.
Analysis of HLA-E expression in human tumors 总被引:9,自引:1,他引:8
Marín R Ruiz-Cabello F Pedrinaci S Méndez R Jiménez P Geraghty DE Garrido F 《Immunogenetics》2003,54(11):767-775
959.
Takenaka S Okugawa S Kadowaki M Murakami S Aoki K 《Applied and environmental microbiology》2003,69(9):5410-5413
Burkholderia sp. strain AK-5 utilized 4-aminophenol as the sole carbon, nitrogen, and energy source. A pathway for the metabolism of 4-aminophenol in strain AK-5 was proposed based on the identification of three key metabolites by gas chromatography-mass spectrometry analysis. Strain AK-5 converted 4-aminophenol to 1,2,4-trihydroxybenzene via 1,4-benzenediol. 1,2,4-Trihydroxybenzene 1,2-dioxygenase cleaved the benzene ring of 1,2,4-trihydroxybenzene to form maleylacetic acid. The enzyme showed a high dioxygenase activity only for 1,2,4-trihydroxybenzene, with K(m) and V(max) values of 9.6 micro M and 6.8 micro mol min(-1) mg of protein(-1), respectively. 相似文献
960.
Nozhevnikova AN Zepp K Vazquez F Zehnder AJ Holliger C 《Applied and environmental microbiology》2003,69(3):1832-1835
In order to obtain evidence for the existence of psychrophilic methanogenic communities in sediments of deep lakes that are low-temperature environments (4 to 5 degrees C), slurries were first incubated at temperatures between 4 and 60 degrees C for several weeks, at which time they were amended, or not, with an additional substrate, such as cellulose, butyrate, propionate, acetate, or hydrogen, and further incubated at 6 degrees C. Initial methane production rates were highest in slurries preincubated at temperatures between 4 and 15 degrees C, with maximal rates in slurries kept at 6 degrees C. Hydrogen-amended cultures were the only exceptions, with the highest methane production rates at 6 degrees C after preincubation at 30 degrees C. 相似文献