REDOX PROPERTIES OF ARSENATE REDUCTASE FROM SYNECHOCYSTIS SP. PCC6803

Abstract

In the environment, arsenate is commonly encountered at biologically deleterious concentrations. Microbes combat the collateral importation of arsenate by a two‐step mechanism: first, arsenate reductase reduces the compound to arsenite, which the cell subsequently exports via an inducible, transmembrane transporter. The redox properties of the arsenate reductase and a glutaredoxin from the cyanobacterium Synechocystis sp. PCC6803 have been investigated. Using mBBr (monobromobimane) and AMS (4‐acetamido‐4′‐maleimidylstibene‐2,2′‐disulfonic acid), redox titrations indicated one active dithiol/disulfide coupling with midpoint potentials of ‐140 mV for the arsenate reductase and ‐160 mV for the glutaredoxin. The interaction between arsenate reductase and glutaredoxin are also observed by using gel filtration. These findings suggest that glutaredoxin's donation of an electron pair to the arsenate reductase is a thermodynamically favorable redox reaction. As such, glutaredoxin's reduction capabilities are essential for the activation and proper functioning of arsenate reductase, which in turn is critical for cellular survival.