All plants examined to date possess non-symbiotic hemoglobin whose physiological role remains unclear. The present study explored the catalytic function of three representative classes of the plant hemoglobin from Arabidopsis thaliana: AtGLB1, AtGLB2, and AtGLB3. Purified recombinant proteins of these hemoglobins displayed hydrogen peroxide-dependent oxidation of several peroxidase substrates that was sensitive to cyanide, revealing intrinsic peroxidase-like activity. In the presence of nitrite and hydrogen peroxide, AtGLB1 was the most efficient at mediating tyrosine nitration of its own and other proteins via the formation of reactive nitrogen species as a result of nitrite oxidation. AtGLB1 mRNA significantly accumulated in Arabidopsis seedlings exposed to nitrite, supporting the physiological relevance of its function to nitrite and nitritederived reactive nitrogen species.
We examined the effects of 75 kinds of natural compounds, such as alkaloids, phenylpropanoids, flavonoids, steroids and terpenoids on the in vitro migration and proliferation of colon 26-L5 cells, in comparison with anticancer drugs used for chemotherapy. Twenty-three of the 75 compounds inhibited markedly tumor cell migration. Among the 23 compounds, evodiamine showed the most potent and selective inhibitory activity on tumor cell migration with an IC 50 value of 1.25 m mg/ml, which was about 20 times lower than that for tumor cell proliferation. The migratory inhibition reached about 70% at 10 m mg/ml of evodiamine. On the other hand, most of anticancer drugs tested, except for paclitaxel, had little effect on tumor cell migration at the concentrations strongly inhibiting tumor cell proliferation. Paclitaxel suppressed tumor cell migration in a concentration-dependent manner and achieved about 70% inhibition at 10 m mg/ml with a marginal effect on cell proliferation. These results suggest that evodiamine and paclitaxel may be regarded as leading compounds for anti-metastatic agents acting through the inhibition of tumor cell migration without cytotoxicity.
The dibenzothiophene (DBT)-desulfurizing bacterium, Rhodococcus erythropolis D-1, removes sulfur from DBT to form 2-hydroxybiphenyl using four enzymes, DszC, DszA, DszB, and flavin reductase. In this study, we purified and characterized the flavin reductase from R. erythropolis D-1 grown in a medium containing DBT as the sole source of sulfur. It is conceivable that the enzyme is essential for two monooxygenase (DszC and DszA) reactions in vivo. The purified flavin reductase contains no chromogenic cofactors and was found to have a molecular mass of 86 kDa and four identical 22-kDa subunits. The enzyme catalyzed NADH-dependent reduction of flavin mononucleotide (FMN), and the K m values for NADH and FMN were 208 and 10.8 M, respectively. Flavin adenine dinucleotide was a poor substrate, and NADPH was inert. The enzyme did not catalyze reduction of any nitroaromatic compound. The optimal temperature and optimal pH for enzyme activity were 35°C and 6.0, respectively, and the enzyme retained 30% of its activity after heat treatment at 80°C for 30 min. The N-terminal amino acid sequence of the purified flavin reductase was identical to that of DszD of R. erythropolis IGTS8 (K. A. Gray, O. S. Pogrebinsky, G. T. Mrachko, L. Xi, D. J. Monticello, and C. H. Squires, Nat. Biotechnol. 14:1705-1709, 1996). The flavin reductase gene was amplified with primers designed by using dszD of R. erythropolis IGTS8, and the enzyme was overexpressed in Escherichia coli. The specific activity in crude extracts of the overexpressed strain was about 275-fold that of the wild-type strain.Organic sulfur compounds are found in fossil fuels, the combustion of which causes serious environmental problems, such as acid rain. At the refinery, hydrodesulfurization is currently performed to remove sulfur compounds from fossil fuels. This process is done at high temperatures and pressures by metal catalysis and is effective for removing inorganic sulfur and simple organic sulfur compounds. However, it is difficult to remove polycyclic sulfur compounds. As legislative limits on sulfur emissions have become tighter, the need to remove polycyclic sulfur compounds from fuel has become more pressing. Dibenzothiophene (DBT) is considered a model polycyclic sulfur compound contained in fossil fuels. It has been reported that some bacteria utilize DBT as a sole source of sulfur without breaking its carbon-carbon backbone. This sulfur-specific pathway has been extensively studied by using two Rhodococcus strains, Rhodococcus erythropolis IGTS8 (7, 11, 13) and R. erythropolis D-1 (10, 19, 20). The genes encoding enzymes involved in this pathway have been cloned and sequenced in R. erythropolis IGTS8 (2, 3, 25) and the thermophilic desulfurizing bacterium Paenibacillus sp. strain A11-2 (9). In this pathway, DBT is oxidized to DBT sulfone via DBT sulfoxide by DszC, DBT sulfone is converted to 2Ј-hydroxybiphenyl 2-sulfinic acid (HBPSi) by DszA, and HBPSi is desulfurized to 2-hydroxybiphenyl by DszB (Fig. 1). Flavin reductase is necessary for monooxygenase reac...
Summary We report the unexpected novel finding that exogenously supplied atmospheric NO2 at an ambient concentration is a plant vitalization signal to double shoot size and the contents of cell constituents. When seedlings of Nicotiana plumbaginifolia were grown for 10 wk under natural light and irrigation with 10 mm KNO3 in air containing (+NO2 plants) or not containing (–NO2 plants) 15NO2 (150 ± 50 ppb), shoot biomass, total leaf area, and contents per shoot of carbon (C), nitrogen (N), sulphur (S), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), free amino acids and crude proteins were all approximately 2 times greater in +NO2 plants than in –NO2 plants. In mass spectrometric analysis of the 15N/14N ratio, it was found that NO2‐derived N (NO2‐N) comprised < 3% of total plant N, indicating that the contribution of NO2‐N to total N was very minor. It thus seems very likely that the primary role of NO2 is as a multifunctional signal to stimulate plant growth, nutrient uptake and metabolism.
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