Role of cysteine residues in methylation
of As(III). (A) In vivo methylation of As(III) by
wild-type and mutant hAS3MTs. E. coli BL21(DE3) cells bearing vector pET41a(+)
or plasmids with wild-type or cysteine mutant genes in pET41a-hAS3MT were grown in 2 mL of Luria Broth medium in the presence
of 20 μM As(III), 0.3 mM IPTG, and 50 μg/mL kanamycin
at 37 °C for 12 h. (B) Methylation of As(III) by purified wild-type
and mutant hAS3MTs. Methylation of As(III) was assayed at 37 °C
after 3 h with 10 μM As(III), 1 μM hAS3MT, 1 mM SAM, 5
mM GSH, 10 μM Trx, 3 μM TR, and 0.3 mM NADPH.