Anion permease ArsB/NhaD. These permeases have been shown totranslocate sodium, arsenate, antimonite, sulfate and organicanions across biological membranes in all three kingdoms of life. A typical anion permease contains 8-13 transmembrane helicesand can function either independently as a chemiosmotic transporteror as a channel-forming subunit of an ATP-driven anion pump.

ArsA ATPase functionas as an efflux pump located on the innermembrane of the cell. This ATP-driven oxyanion pump catalyzesthe extrusion of arsenite, antimonite and arsenate. Maintenanceof a low intracellular concentration of oxyanion produces resistanceto the toxic agents. The pump is composed of two subunits, thecatalytic ArsA subunit and the membrane subunit ArsB, which areencoded by arsA and arsB genes respectively. Arsenic efflux inbacteria is catalyzed by either ArsB alone or by ArsAB complex.The ATP-coupled pump, however, is more efficient. ArsA is composedof two homologous halves, A1 and A2, connected by a short linkersequence.

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