Table II. High frequency ions in iTRAQ4 tandem mass spectra.

Rep+: singly charged reporter ion, Label+: singly charged isobaric tagion, Y1(R): y1 ion from peptide with 3′ terminal amino acid R, Y1(K): y1 ion from peptide with 3′ terminal amino acid K, b/y free: ion in the b/y free windows.

Charge	Ion	Count	Frequency	Meana	S.D.b	Medianc	Annotation
2	116.1111	37123	0.997	0.837	0.274	1	Rep+
	115.1078	37101	0.9964	0.744	0.243	0.844	Rep+
	117.1144	37090	0.9961	0.799	0.269	0.934	Rep+
	114.1107	37076	0.9957	0.751	0.253	0.858	Rep+
	145.108	36251	0.9735	0.206	0.114	0.194	Label+
	291.2155	35287	0.9477	0.238	0.183	0.201	Y1(K)
	110.0712	34004	0.9132	0.15	0.196	0.078	b/y free
	175.119	33280	0.8938	0.2	0.202	0.111	Y1(R)
	120.0807	25310	0.6797	0.149	0.194	0.077	b/y free
	158.0924	23172	0.6223	0.076	0.061	0.061	b/y free
	429.0889	15170	0.4074	0.304	0.378	0.087	Unknown
3	116.111	23680	0.9917	0.433	0.256	0.383	Rep+
	115.1077	23666	0.9911	0.399	0.243	0.347	Rep+
	117.1144	23644	0.9902	0.41	0.244	0.363	Rep+
	114.1107	23639	0.99	0.387	0.234	0.339	Rep+
	291.2155	22582	0.9457	0.294	0.247	0.225	Y1(K)
	145.1079	22367	0.9367	0.127	0.092	0.103	Label+
	110.0712	21007	0.8798	0.285	0.309	0.149	b/y free
	175.119	19229	0.8053	0.133	0.119	0.098	Y1(R)
	120.0807	17309	0.7249	0.22	0.266	0.105	b/y free
	429.0888	13624	0.5706	0.261	0.329	0.098	Unknown
	136.0756	13377	0.5602	0.153	0.225	0.06	b/y free
	258.1936	9096	0.3809	0.08	0.082	0.054	Unknown
	404.2996	7790	0.3262	0.167	0.225	0.063	Unknown
	101.0709	7675	0.3214	0.078	0.075	0.05	b/y free
4	115.1077	3570	0.938	0.123	0.089	0.101	Rep+
	116.111	3566	0.9369	0.131	0.089	0.112	Rep+
	117.1144	3552	0.9333	0.125	0.085	0.107	Rep+
	114.1107	3533	0.9283	0.118	0.083	0.099	Rep+
	291.2155	3287	0.8636	0.178	0.197	0.103	Y1(K)
	110.0712	2770	0.7278	0.216	0.257	0.103	b/y free
	120.0808	2314	0.608	0.181	0.238	0.082	b/y free
	429.0888	1976	0.5192	0.255	0.333	0.087	Unknown
	163.1188	1659	0.4359	0.249	0.333	0.062	b/y free
	136.0756	1594	0.4188	0.15	0.221	0.056	b/y free

^a mean of relative abundance.

^b stand deviation of relative abundance.

^c median of relative abundance.