FIGURE 7.

Assay for ethidium efflux by whole cells of E. coli CM2 transformants. Ethidium efflux assay was carried out by using the whole cells of E. coli CM2 transformants carrying pET-mdrP and the empty vector pET19b (as a negative control). CCCP was used at a final concentration of 40 μM for the depletion of cell energy and energy-starved cells were pre-loaded with ethidium bromide at a final concentration of 2.5 μM. After 1 min (downward arrow), glucose was added to cell suspensions at a final concentration of 20 mM to re-energize cells. The efflux of intracellular ethidium was monitored continuously by measuring the fluorescence of ethidium at the excitation and emission wavelengths of 500 and 580 nm, respectively.