Characterization of 2-bromoethanesulfonate as a selective inhibitor of the coenzyme M-dependent pathway and enzymes of bacterial aliphatic epoxide metabolism

Bacterial growth with short-chain aliphatic alkenes requires coenzyme M (CoM) (2-mercaptoethanesulfonic acid), which serves as the nucleophile for activation and conversion of epoxide products formed from alkene oxidation to central metabolites. In the present work the CoM analog 2-bromoethanesulfonate (BES) was shown to be a specific inhibitor of propylene-dependent growth of and epoxypropane metabolism by Xanthobacter autotrophicus strain Py2. BES (at low [millimolar] concentrations) completely prevented growth with propylene but had no effect on growth with acetone or n-propanol. Propylene consumption by cells was largely unaffected by the presence of BES, but epoxypropane accumulated in the medium in a time-dependent fashion with BES present. The addition of BES to cells resulted in time-dependent loss of epoxypropane degradation activity that was restored upon removal of BES and addition of CoM. Exposure of cells to BES resulted in a loss of epoxypropane-dependent CO, fixation activity that was restored only upon synthesis of new protein. Addition of BES to cell extracts resulted in an irreversible loss of epoxide carboxylase activity that was restored by addition of purified 2-ketopropyl-CoM carboxylase/oxidoreductase (2-KPCC), the terminal enzyme of epoxide carboxylation, but not by addition of epoxyalkane:CoM transferase or 2-hydroxypropyl-CoM dehydrogenase, the enzymes which catalyze the first two reactions of epoxide carboxylation. Comparative studies of the propylene-oxidizing actinomycete Rhodococcus rhodochrous strain B276 showed that BES is an inhibitor of propylene-dependent growth in this organism as well but is not an inhibitor of CoM-independent growth with propane. These results suggest that BES inhibits propylene-dependent growth and epoxide metabolism via irreversible inactivation of the key CO2-fixing enzyme 2-KPCC.