Arsenicals Methylation Reaction Assay

Arsenicals, iAs (Sigma S7400, NaAsO₂, purity equal or more than 90%) prepared as a 10 mM stock in ddH₂O was further diluted in H₂O to the desired concentrations. Methyl arsonous acid (MAs III; 0.37 mg/L) synthesis was performed as previously described (Negro Silva et al. 2021 (link)) and its stock concentration was 25 mM. DMA (Sigma C4945, Sodium cacodylate trihydrate, (CH₃)₂AsO₂Na 3H₂O) stock was 10 mM in ddH₂O. Rat liver cofactors thioredoxin (TRX, Sigma T0910) and thioredoxin reductase were purchased from Sigma (TRR, Sigma T9698), and L-glutathione reduced (GSH, Sigma G6529), NADPH (Sigma 10107824001), DTT, Adenosyl-L-Methionine (SAM), and S-[methyl-³H] (SAM [³H], PerkinElmer). Human recombinant histones H2A, H2B, H3, and H4 were purchased from New England Biolabs.