Fig. 4.

Sulfenylation of Cys181 of AtMAPK4 that is crucial for the kinase activity. (A) S-sulfenylation of the H₂O₂-sensitive Cys in the MAP kinase signature (PS01351 PROSITE pattern) in Arabidopsis (Cys176 in AtMAPK3; Cys181 in AtMAPK4; Cys201 in AtMAPK6; and Cys178 in AtMAPK11) and human (Cys161 in HsMAPK1). (B) Dimedone blot showing AtMAPK4 S-sulfenylation under 1 mM H₂O₂ for 1 h. (C). Annotated spectrum match of ‘DLKPSNLLLNANC₁₈₁DLK’ with Cys181 modified by dimedone (+138.0 Da). (D) Kinase activity of AtMAPK4 and its C181S variant as measured on phosphorimage displaying myelic basic protein (MBP) phosphorylation with [³²P]ATP. (E) Kinase activity of autophosphorylated (P_i) and nonautophosphorylated AtMAPK4 and its C181S variant as measured by quantitative Cerenkov counting after 45 min of incubation with MBP.