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Recruitment of Enzymes to Serve New Functions in a Newly Evolving Metabolic Pathway

Joe Warner
Copley Lab, CIRES
Boulder, Colorado

The pathway for degradation of the xenobiotic pesticide pentachlorophenol in Sphingobium chlorophenolicum probably evolved in the past few decades by the recruitment of enzymes from other catabolic pathways. The first and fourth enzymes in the pathway, pentachlorophenol hydroxylase and 2,6-dichlorohydroquinone dioxygenase, may have originated from enzymes in a pathway for degradation of a naturally occurring chlorinated phenol. The second enzyme in the pathway, tetrachlorobenzoquinone reductase, is most closely related to the reductase components of 2-component dioxygenases. The third enzyme, a reductive dehalogenase, may have evolved from a maleylacetoacetate isomerase normally involved in degradation of tyrosine. This recently assembled pathway does not function very well. Pentachlorophenol hydroxylase is quite slow and the reductive dehalogenase is profoundly inhibited by its own substrate. The biodegradation pathway of pentachlorophenol is an example of how enzymes may be recruited from places we would never predict.