Involvement of Cysteine Residues in the Function and Inactivation of PCP Hydroxylase

Undergraduate Honors Thesis

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/2514nm03w

Abstract

The alteration of a microbial environment by introduction of a new xenobiotic chemical leads to the evolution of new metabolic pathways so that the microbes can detoxify them and utilize them as carbon sources. Pentachlorophenol (PCP) is a toxic pollutant that was introduced into the environment in the 1930’s. The Gram-negative bacterium Sphingobium chlorophenolicum strain [L-1 ATCC 53874] was isolated from soil contaminated with PCP and has been observed to be able to degrade PCP. The first enzyme in the PCP degradation pathway in this bacterium, PCP hydroxylase, catalyzes the rate-limiting step in the pathway. Along with its poor efficiency, this enzyme is inactivated by its product, tetrachlorobenzoquinone (TCBQ). It is suggested that this inactivation occurs as a result of the covalent attachment of TCBQ to cysteine residues on the enzyme. I have found that changing cysteine residues 302 and 537 to serines does not significantly affect the activity of the enzyme, and changing cysteine residue 537 to serine slightly reduced the degree of inactivation by TCBQ. The C537S mutant version of the enzyme was about three-fold inactivated, while the wild type version was about four-fold inactivated.

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