CHARACTERIZATION OF MUCONATE AND CHLOROMUCONATE CYCLOISOMERASE FROM RHODOCOCCUS-ERYTHROPOLIS 1CP - INDICATIONS FOR FUNCTIONALLY CONVERGENT EVOLUTION AMONG BACTERIAL CYCLOISOMERASES

Muconate cycloisomerase (EC 5.5.1.1) and chloromuconate cycloisomerase (EC 5.5.1.7) were purified from extracts of Rhodococcus erythropolis 1CP cells grown with benzoate or 4-chlorophenol, respectively. Both en zymes discriminated between the two possible directions of 2-chloro-ci s,cis-muconate cycloisomerization and converted this substrate to 5-ch loromuconolactone as the only product. In contrast to chloromuconate c ycloisomerases of gram-negative bacteria, the corresponding R. erythro polis enzyme is unable to catalyze elimination of chloride from (+)-5 -chloromuconolactone. Moreover, in being unable to convert (+)-2-chlor omuconolactone, the two cycloisomerases of R. erythropolis 1CP differ significantly from the known muconate and chloromuconate cycloisomeras es of gram-negative strains. The catalytic properties indicate that ef ficient cycloisomerization of 3-chloro- and 2,4-dichloro-cis,cis-mucon ate might have evolved independently among gram-positive and gram-nega tive bacteria.