Reactions of 3-ethylcatechol and 3-(methylthio)catechol with catechol dioxygenases

The reactions of 3-ethylcatechol and 3-(methylthio)catechol with catechol 1,2-dioxygenase and catechol 2,3-dioxygenase from Pseudomonas putida were examined. Both 3-substituted catechols are oxidized by catechol 2,3-dioxygenase at approximately 30% of the rate observed for catechol oxidation by this enzyme. Analysis of the products of the reactions showed that ring cleavage occurs in a normal fashion between carbons 2 and 3 of the alternate substrates. 3-Ethylcatechol is oxidized by catechol 1,2-dioxygenase at about 6% of the rate of catechol oxidation; ring cleavage occurs between carbons 1 and 2 to give 2-ethyl-cis,cis-muconic acid. However, 3-(methylthio)catechol is a very poor substrate for catechol 1,2-dioxygenase (0.8% of the rate of catechol), but it is a potent competitive inhibitor (Ki = 0.6 microM). The effects of 3-(methylthio)catechol and 3-ethylcatechol on the visible and EPR spectra of catechol 1,2-dioxygenase are also reported.