Abbau und Biosynthese von L-Phenylalanin in Chloridazon-abbauenden Bakterien

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Abstract
Incubating chloridazon-degrading bacteria with L-phenylalanine leds to the accumulation of L-2,3-dihydroxyphenylalanine, o-tyrosine and m-tyrosine in the medium. Incubating the bacteria with N-acetyl-L-phenylalanine leds to N-acetyl-(2,3-dihydroxyphenyl)alanine. Using phenylacetic acid as substrate leds to the accumulation of malonic acid. The products were isolated by gel chromatography and high performance liquid chromatography. 2,3-Dihydroxy-L-phenylalanine was attacked by a catechol 2,3-dioxygenase in the presence of Fe2+. An unstable yellow compound was formed in this reaction. This meta-cleavage-product was again cleaved by a hydrolase, leading to aspartic acid and 4-hydroxy-2-oxovaleric acid. Both products were isolated from the reaction buffer by amino acid analysis and high performance liquid chromatography. The dioxygenase and hydrolase were partially purified and characterized. A new degradation pathway for phenylalanine is disucssed and compared with known pathways. The enzymes chorismate mutase, prephenate dehydratase and prephenate dehydrogenase were characterized and inhibition and repression were investigated. Only prephenate dehydrogenase was inhibited by phenylalanine, tyrosine and tryptophane. Chorismate mutase was repressed by phenylalanine, prephenate dehydrogenase by phenylalanine and tyrosine. Prephenate dehydratase was not repressed by aromatic amino acids. Regulation of aromatic amino acid biosynthesis in connnection with phenylalanine degradation is discussed.