Basic analysis and development of novel lactonases promising for industrial catalysts

点击翻译按钮获取中文摘要

Microbial lactonases (lactone-ring-cleaving enzymes) with unique characteristics were found. The Fusarium oxysporum enzyme catalyzes the reversible and stereospecific hydrolysis of aldonate lactones and D-pantolactone (D-PL), and is useful for the optical resolution of racemic PL. The Agrobacterium tumefaciens enzyme hydrolyzes several aromatic lactones, and catalyzes the stereospecific hydrolysis of PL like the Fusarium enzyme, but its selectivity is opposite. The Acinetobacter calcoaceticus enzyme catalyzing the specific hydrolysis of dihydrocoumarin belongs to serine-enzyme family, and is useful for enantioselective hydrolysis of methyl DL-β-acetylthioisobutyrate and regioselective hydrolysis of methyl cetraxate. This enzyme also catalyzes the bromination of monochlorodimedon when incubated with H_2O_2 and dihydrocoumarin.The physiological role of a bifunctional enzyme, dihydrocoumarin hydrolase of A. calcoaceticus was investigated. Purified enzyme from A. calcoaceticus catalyzed do … More se- and time-dependent degradation of peracetic acid. The gene (dch) was cloned from the chromosomal DNA of the bacterium. The open reading frame of dch was 831 bp long, corresponding to a protein of 272 amino acid residues, and deduced amino acid sequence showed high similarity to those of bacterial serine-esterases and noheme haloperoxidases. The dch gene was disrupted by homologous recombination on the A. calcoaceticus genome. The dch disruptant strain was more sensitive to growth inhibition by peracetic acid than the parent strain. On the other hand, recombinant E. coli cells expressing dch were more resistant to peracetic acid. The putative catalase gene was found immediately downstream of dch, and Nothern hybridization analysis revealed that both of them were transcript as part of a polycistronic mRNA. These results suggested that dihydrocoumarin hydrolase in vivo detoxified peroxoacids in conjunction with the catalase, i.e. at first, peroxoacids are hydrolyzed to the corresponding acids and hydrogen peroxide by dihydrocoumarin hydrolase, and then the resulting hydrogen peroxide is degraded by the catalase. Less