Stereo- and regiospecific cis,cis-muconate cycloisomerization by Rhodococcus rhodochrous N75

cis,cis-Muconate cycloisomerase was purified to homogeneity from cells of Rhodococcus rhodochrous N75 grown at the expense of benzoate and p-toluate as the sole sources of carbon. A single cycloisomerase was found to be induced in this organism with no isoforms being detected when R. rhodochrous N75 was grown on either benzoate or p-toluate as the sole source of carbon. The enzyme is hexameric with a single subunit Mr of 40,000. cis,cis-Muconate cycloisomerase from R. rhodochrous N75 displayed strict regio- and stereospecificity whereby cis,cis-muconate is cycloisomerized to (4S)-muconolactone and 2-methyl- and 3-methyl-substituted muconates are cycloisomerized to 2-methyl- and 4-methyl-substituted muconolactones by 1,4- and 3,6-cycloisomerization, respectively.