FIGURE 4.

Identification of Ser-449 of Kv1.2 as a site of phosphorylation after in vitro PKA treatment. ³²P-Labeled tryptic peptides of Kv1.2-WT-myc after in vitro PKA treatment were partially purified on a C18 column and analyzed by mass spectrometry. A, ion trap full scan MS spectrum of Kv1.2-myc tryptic digest showing a major phosphopeptide with m/z 773.4. B, MS/MS spectrum resulting from isolation and collision-induced fragmentation of the singly charged m/z 773.4 precursor ion. The sequence of the m/z 773.4 ion shown is based on a y-ion series (separated by vertical lines). amu, atomic mass units; Sp, phosphoserine.