Involved in resistance to arsenate. Catalyzes the reduction of arsenate [As(V)] to arsenite [As(III)]. The resulting arsenite is then extruded from the cell via the aquaglyceroporin AqpS. Does not display antimonate reductase activity. [glutaredoxin]-dithiol + arsenate + glutathione + H(+) = arsenite + glutathionyl-S-S-[glutaredoxin] + H2O Disruption mutant shows selective sensitivity to arsenate. Does not affect sensitivity to antimonate [Sb(V)]. Belongs to the ArsC family.