Evolution of a metabolic pathway for degradation of a toxic xenobiotic: the patchwork approach

The pathway for degradation of the xenobiotic pesticide pentachlorophenol i n Sphingomonas chlorophenolica probably evolved in the past few decades by the recruitment of enzymes from two other catabolic pathways. The first and third enzymes in the pathway, pentachlorophenol hydroxylase and 2,6-dichlo rohydroquinone dioxygenase, may have originated from enzymes in a pathway f or degradation of a naturally occurring chlorinated phenol. The second enzy me, a reductive dehalogenase, may have evolved from a maleylacetoacetate is omerase normally involved in degradation of tyrosine. This apparently recen tly assembled pathway does not function very well: pentachlorophenol hydrox ylase is quite slow, and tetrachlorohydroquinone dehalogenase is subject to severe substrate inhibition.