ナイロンオリゴマー分解系酵素の性質とその遺伝子構造
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概要
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1. 6-Aminohexanoate-cyclic-dimer hydrolase (EI), exotype 6-aminohexanoate-oligomer hydrolase (EII), and endotype 6-aminohexanoate-oligomer hydrolase (EIII) were found to be responsible for Flavobacterium sp. KI72 degrading 6-aminohexanoate-oligomers, by-products of nylon-6-manufacture. 2. The genes for the EI (F-nylA), EII (F-nylB), and EIII (nylC) were encoded on pOAD2,one of the three plasmids harbored in Flavobacterium sp. KI72. This plasmid contains two repeated sequences, RS-I and RS-II; one of the two RS-II regoins, RS-II_A, contains the F-nylB gene, while the other, RS-II_B, contains the homologous EII' gene (nylB'). The F-nylB and nylB' have 88% similarity in their nucleotide sequences, an open reading frame encoding a polypeptide of 392 amino acids. Catalytic activity of the EII' protein toward 6-aminohexanoate-dimer was approximately 0.5% of that of the EII enzyme. 3. Construction of various hybrid genes obtained by exchanging fragments flanked by conserved restriction sites of the F-nylB and nylB' genes demonstrated that two amino acid replacements in the EII' enzyme, i.e. Gly181→Asp (EII type) and His266→Asn (EII typ), enhanced the activity toward 6-aminohexanoate-dimer 200 fold. 4. The EI and EII enzymes were found in another 6-aminohexanoate-cyclic dimer degrading bacterium, Pseudomonas sp. NK87. The EI gene (P-nylA) and EII gene (P-nylB) of NK87 strain were located on the 23-kilo-base pairs (kbp) and 80-kbp plasmids, respectively. The F-nylA and P-nylA genes encoded polypeptide of 493 amino acids and had 10 base substitutions in the coding region. In contrast to the high homology of the nylA genes, the F-nylB and P-nylB genes had only 55% similarity in the nucleotide sequences, and 35% similarity in the deduced amino acid sequences. On the basis of the structure of nylA, nylB and nylC genes, we discussed how nylon oligomer degradation genes were evolved.
- 社団法人日本生物工学会の論文
- 1992-03-25