MsrA catalyzes the DMS‐mediated scavenging of radicals via formation of sulfonium intermediate at residues Cys72, Tyr103, Glu115. (A) DMS could easily bind to the catalytic pocket of MsrA, which is composed of side chains of Cys72, Phe73, Trp74, Tyr103, and Glu115. (B) Steady‐state fluorescence anisotropy values are shown as a function of increased concentrations of DMS. The concentration of MsrA was 3 μm. (C) The effect of 0.1 mm DMS on the signal intensity of DMPO‐OH adducts in the presence of MsrA or nonactive MsrA was evaluated under the same experimental conditions (n = 5, Student's t‐test, **P < 0.01 vs. no enzyme group). The peak intensity of EPR was expressed as a relative change in comparison with 0.1 mm DMS treatment, which was set to 100%. (D) The transform rate of DMS into DMSO in the presence of active MsrA or nonactive MsrA was determined by GC‐MS method (n = 6, Student's t‐test, **P < 0.01 vs. control). (E) The catalytic activity of single site mutant enzymes was detected by the reaction of scavenging OH˙ radicals. The activity of native enzyme was set as 100%, and boiled enzyme was set as negative control (n = 6, **P < 0.01 vs. control, Student's t‐test). Data are expressed as mean ± SEM.