ブラストサイジンSおよびメトキシフェノンの代謝分解に関する研究

抄録

The behavior and metabolism of blasticidin S and methoxyphenone were studied in the model system to evaluate their safety in the environment. ¹⁴C-blasticidin S was prepared biosynthetically by the producing organism, St. griseochromogenes. Prior to the study on the metabolism of blasticidin S, its site for accumulation was investigated to find that the antibiotic was mostly located on the surface of the rice plant after foliar application. From the wound or infected part, however, blasticidin S was uptaken by the plant and was translocated mainly to the upper part. The compound on the plant surface was decomposed by sunlight and gave rise to cytosine as the main degradation product. In the plant the antibiotic was metabolized gradually, and a small amount of cytomycin and trace of others were produced. A considerable quantity of blasticidin S was supposed to fall on the ground by rainfall besides those fallen when it was sprayed, which was found to be bound firmly onto the soil surface. From ¹⁴C-blasticidin S-treated soil significant liberation of ¹⁴CO₂ was observed, and several microbes usually inhabiting in the paddy field were involved in lowering the biological activity of blasticidin S. Among the microbes, an isolated fungal strain, which was identified as Asp. terreus, caused marked inactivation by converting the antibiotic to deaminohydroxy-derivative. The enzyme was isolated and characterized to be a new aminohydrolase. Methoxyphenone was readily metabolized in the treated plants, in soils, and by rats. Products oxidized at 3 or 3′-CH₃, a 4-desmethyl metabolite, and a reduced one at carbonyl group were identified as metabolites in common by using ¹⁴C-methoxyphenone labeled at carbonyl carbon. There were observed some differences in metabolism in each system, e. g., ¹⁴CO₂ was liberated only from a treated soil. An isolated bacterium (Bacillus sp.) capable of degrading methoxyphenone showed a remarkable activity to phosphorylate phenolic OH of the desmethylated metabolite.