RGS18 phosphorylation induced by TRAP. (A) 2-DE gel images showing the RGS18 features. (B) MS/MS spectrum of the ion at m/z 541.24 (4+), corresponding to NRLS*LLVQKPEFHEDTR (* indicates phosphorylated). All the b and a ions presented in the spectrum (except b₂) appear after the loss of 98 Da from the phosphate group during fragmentation.