The mechanism of the polynucleotide phosphorylase-catalyzed arsenolysis of ADP

► From ADP and arsenate, PNPase forms AMP-arsenate, which is hydrolyzed (arsenolysis). ► Polynucleotide phosphorylase (PNPase) does not catalyze ADP arsenolysis directly. ► Polynucleotide phosphorylase (PNPase) catalyzes the arsenolysis of ADP in two steps. ► PNPase polymerizes ADP to poly-A then cleaves poly-A with arsenate to AMP-arsenate. ► In presence of glutathione, the PNPase-generated AMP-arsenate is reduced to arsenite.