Mechanisms of active transport in isolated bacterial membrane vesicles

Carbonylcyanide m -chlorophenylhydrazone, a well-known uncoupling agent, inhibits lactose and amino acid transport by isolated cytoplasmic membrane vesicles from Escherichia coli and Staphylococcus aureus in the micromolar concentration range and has many of the properties of a typical sulfhydryl reagent. Its inhibitory effects are not alleviated by dilution and washing, but the addition of a number of thiol compounds, dithiothreitol in particular, dramatically blocks and reverses its inhibitory activity. Moreover, incubation of vesicles with this uncoupler diminishes their reactivity towards N -ethylmaleimide, suggesting that the compound blocks sulfhydryl groups in membrane proteins. Neither of these effects are observed with 2,4-dinitrophenol. The results are discussed in terms of chemical and chemiosmotic concepts of energy transduction.