DUAL-MODE OF ENERGY COUPLING BY THE OXYANION-TRANSLOCATING ARSB PROTEIN

The arsA and arsB genes of the ars operon of R-factor R773 confer arsenite resistance in Escherichia coli by coding for an anion-translocating ATPase. Arsenite resistance and the in vivo energetics of arsenite transport were compared in cells expressing the arsA and arsB genes and those expressing just the arsB gene. Cells expressing the arsB gene exhibited intermediate arsenite resistance compared with tells expressing both the arsA and arsB genes. Both types of cells exhibited energy-dependent arsenite exclusion. Exclusion of (AsO2-)-As-73 from cells expressing only the arsB gene was coupled to electrochemical energy, while in cells expressing both genes, transport was coupled to chemical energy, most likely ATP. These results suggest that the Ars anion transport system can be either an obligatory ATP-coupled primary pump or a secondary carrier coupled to the proton motive force, depending on the subunit composition of the transport complex.