- Evidence that pcpA encodes 2,6-dichlorohydroquinone dioxygenase, the ring cleavage enzyme required for pentachlorophenol degradation in Sphingomonas chlorophenolica strain ATCC 39723. Xu, L., Resing, K., Lawson, S.L., Babbitt, P.C., Copley, S.D. Biochemistry (1999)