Table 3. Characterization by MALDI–TOF MS and ESI-MS/MS of N-terminal PIP2 peptides from a root PM extract.

The Table shows putative PIP2 peptides that were identified from the 28 kDa band of a root PM fraction as described in Table 2. Peptides with modified residues are indicated in boldface characters. Conventions for post-translational modifications are as follows: 1me, monomethyl; 2me, dimethyl; _1meE6, monomethyl Glu⁶; _2meK3, dimethyl Lys³.

Measured mass (Da) [M+H]+	Predicted peptide sequence	Determined peptide sequence	Modification	Isoform	Position in the sequence
886.46	KWSFYR		None	PIP2;1/PIP2;6	34–39/33–38
1234.56	DVEGPEGFQTR		None	PIP2;2	4–14
1340.65	DLDVNESGPPAAR		None	PIP2;4	4–16
1404.70	DVEAVPGEGFQTR	DVEAVPGEGFQTR	None	PIP2;1	4–16
1418.70	DVEAVPGEGFQTR+14 Da		1me	PIP2;1	4–16
1433.70	AKDVEGPEGFQTR	Tag PEGFQTR	M1 cleaved	PIP2;2	2–14
1447.70	AKDVEGPEGFQTR+14 Da		M1 cleaved+1me	PIP2;2	2–14
1461.70	AKDVEGPEGFQTR+28 Da		M1 cleaved+2me	PIP2;2	2–14
1475.70*	AKDVEGPEGFQTR+42 Da	AKDVEGPEGFQTR	M1 cleaved+2meK3+1me	PIP2;2	2–14
1539.78	AKDLDVNESGPPAAR		M1 cleaved	PIP2;4	2–16
1603.80	AKDVEAVPGEGFQTR	AKDVEGPEGFQTR	M1 cleaved	PIP2;1	2–16
1617.80	AKDVEAVPGEGFQTR+14 Da		M1 cleaved+1me	PIP2;1	2–16
1631.80†	AKDVEAVPGEGFQTR+28 Da	AKDVEAVPGEGFQTR	M1 cleaved+2meK3	PIP2;1	2–16
1645.80†	AKDVEAVPGEGFQTR+42 Da	AKDVEAVPGEGFQTR	M1 cleaved+2meK3+1meE6	PIP2;1	2–16
1869.93	DYVDPPPAPLLDMGELK		None	PIP2;7	16–32
1872.90	DYQDPPPAPFIDGAELK	DYQDPPPAPFI/LDGAELK	None	PIP2;1	17–33
2000.99	DYQDPPPAPFIDGAELKK	DYQDPPPAPFI/LDGAEL/IKK	None	PIP2;1	17–34
2066.96	DYKDPPPAPFFDMEELR		None	PIP2;4	17–33
2096.94	DYEDPPPTPFFDADELTK	DYEDPPPTPFFDADEL/ITK	None	PIP2;2	15–32

*The peptide sequence was deduced from PSD fragmentation. Lys³ was shown to be dimethylated (_2meK3). The additional 14 Da mass increment indicates the presence of a methyl group that must be positioned within the following sequence DVEGPEGFQTR.

†Peptide, the ESI-MS/MS spectrum of which is shown in Figure 2.