Table I.

Yield of Ser during N-terminal sequencing of a phosphorylated and non-phosphorylated synthetic peptide

Residue No.Amino AcidYield of Ser
Peak 1Peak 2Peak 3
 6 [24]Arg5.63.84.3
 7 [25]Ser49 (100)54 (100)52 (100)
 8 [26]Ser45 (92)37 (68)22 (44)
 9 [27]Val6.79.27.8
10 [28]Ser28 (57)7.8 (14)17 (33)
11 [29]Ile4.63.68.1
12 [30]Val2.12.54.0

A synthetic peptide corresponding to A19 to M39 in BCA1p was phosphorylated with PKC, subjected to reverse-phase HPLC (Fig. 7), and the first 12 residues of peaks 1 to 3 were N-terminally sequenced. The yield of Ser-28 in radio-labeled peak 2 (underlined) was significantly lower than in peak 1 (non-radioactive), indicating that it was phosphorylated. Numbers in brackets correspond to the amino acid position in BCA1p. Numbers in parentheses are the percentage yield of Ser-26 and Ser-28 relative to the yield of Ser-25, which was set to 100%. Values for peak 3 have been multiplied with 1.7 to compensate for the lower amount of peptide subjected to sequencing.