To find new extradiol dioxygenases（EDOs,EC 1.13.11.2）,a metagenomics library was constructed from polychlorinated biphenyl-contaminated soil and was screened for some dioxygenase with aromatic ring cleavage activity.A novel EDO,designated as BphC_A,was identified and heterologously expressed in Escherichia coli.The deduced amino acid sequence of BphC_A exhibited a homology of less than 60% with other known EDOs.Phylogenetic analysis of BphC_A suggests that the protein is a novel member of the EDO family.The enzyme exhibits higher substrate affinity and catalytic efficiency toward 3-methylcatechol than toward 2,3-dihydroxybiphenyl or catechol,the preferred substrate of other known EDOs.The optimum activity of purified BphC_A occurred at pH=8.5 and 35 °C,and BphC_A showed more than 40% of its initial activity at 5 °C.The activity of purified BphC_A was significantly induced by Mn^2＋ and slightly reduced by Al^3＋,Cu^2＋ and Zn^2＋.
