Table IX. Unidentified modifications from “blind Search.” All data from Orbitrap runs; all cysteines are alkylated; the bolded residue is the probable location of the modification with mass given in delta mass column. MRAB, median relative abundance; PIIF, peptide identification frequency. Rank, based on peptide identification significance, PSIG.

Rank	PSIG	Observed m/z	z	Sequence	Delta mass	MRAB	PIIF	Possible modification
1	0.09	561.242	3	QNCELFEQLGEYK	23.957	0.0110	0.72
2	0.09	554.913	3	AAFTECCQAADK	291.156	0.0125	0.60
3	0.07	432.215	3	AVMDDFAAFVEK	−48.005	0.0086	0.41	Dethiomethyl
4	0.07	462.215	2	DDNPNLPR	−17.0254	0.0068	0.68	−NH3
5	0.06	836.099	3	ALVLIAFAQYLQQCPFEDHVK	15.996	0.0084	0.45	Oxidation
6	0.06	528.938	3	LKECCEKPLLEK	37.941	0.0059	0.61	+Ca (position?)
7	0.06	839.840	2	QNCELFEQLGEYK	20.919	0.0060	0.58
8	0.05	539.600	3	LKECCEKPLLEK	69.988	0.0038	0.75	+C3H2S
9	0.04	501.287	3	HPDYSVVLLLR	190.105	0.0051	0.40
10	0.04	453.210	2	DDNPNLPR	−35.037	0.0023	0.57	−(H2O + NH3)
11	0.04	417.540	3	FKDLGEENFK	23.953	0.0027	0.49
12	0.04	632.778	2	FKDLGEENFK	37.944	0.0022	0.66	+Ca (from search of unidentified mod.)
13	0.03	462.848	3	ETYGEMADCCAK	−48.005	0.0020	0.48	CH4S
14	0.03	497.937	3	HPDYSVVLLLR	180.053	0.0018	0.48
15	0.02	472.271	2	FQNALLVR	−17.027	0.0010	0.50	−NH3 (position?)
16	0.02	502.257	2	LCTVATLR	69.988	0.0011	0.41	+C3H2S
17	0.02	652.377	2	LVAASQAALGL	290.147	0.0009	0.48
18	0.01	633.803	2	FKDLGEENFK	39.994	0.0004	0.40	C2O