Evidence that pcpA encodes 2,6-dichlorohydroquinone dioxygenase, the ring cleavage enzyme required for pentachlorophenol degradation in Sphingomonas chlorophenolica strain ATCC 39723

An enzyme that catalyzes an Fe2+-dependent reaction of 2,6-dichlorohydroqui none with O-2 has been isolated from Sphingomonas chlorophenolica sp. strai n ATCC 39723, a soil microorganism capable of complete mineralization of pe ntachlorophenol. The product of the reaction is too unstable to allow spect roscopic characterization, but is apparently negatively charged and retains the two chlorine atoms of the substrate, The enzyme was partially sequence d using electrospray LC-MS, and one peptide was used to search the NCBInr d atabase. This peptide matched a part of PcpA, a protein of unknown function that is induced in S. chlorophenolica in response to pentachlorophenol. Se veral other peptides could also be mapped onto the sequence of PcpA, sugges ting that the enzyme is encoded by pcpA. PcpA has lour but significant sequ ence similarity to an unusual class of estradiol dioxygenases, On the basis of the sequence analysis, the Fe2+ and O-2 dependence of the enzyme, and t he characteristics of the product, the enzyme is proposed to be a 2,6-dichl orohydroquinone dioxygenase. The position of ring cleavage has not yet been identified.