Anion permease ArsB/ NhaD. These permeases have been shown to

2. ArsA ATPase functionas as an efflux pump located on the inner membrane of the cell. This ATP-driven oxyanion pump catalyzes the extrusion of arsenite, antimonite and arsenate. Maintenance of a low intracellular concentration of oxyanion produces resistance to the toxic agents. The pump is composed of two subunits, the catalytic ArsA subunit and the membrane subunit ArsB, which are encoded by arsA and arsB genes respectively. Arsenic efflux in bacteria is catalyzed by either ArsB alone or by ArsAB complex. The ATP-coupled pump, however, is more efficient. ArsA is composed of two homologous halves, A1 and A2, connected by a short linker sequence. Anion permease ArsB/NhaD. These permeases have been shown to translocate sodium, arsenate, antimonite, sulfate and organic anions across biological membranes in all three kingdoms of life. A typical anion permease contains 8-13 transmembrane helices and can function either independently as a chemiosmotic transporter or as a channel-forming subunit of an ATP-driven anion pump.

3. Arsenate Reductase (ArsC) family, ArsC subfamily; arsenic reductases similar to that encoded by arsC on the R733 plasmid of Escherichia coli. E. coli ArsC catalyzes the reduction of arsenate [As(V)] to arsenite [As(III)], the first step in the detoxification of arsenic, using reducing equivalents derived from glutathione (GSH) via glutaredoxin (GRX). ArsC contains a single catalytic cysteine, within a thioredoxin fold, that forms a covalent thiolate-As(V) intermediate, which is reduced by GRX through a mixed GSH-arsenate intermediate. This family of predominantly bacterial enzymes is unrelated to two other families of arsenate reductases which show similarity to low-molecular-weight acid phosphatases and phosphotyrosyl phosphatases.