Table 3:

The most frequent precursor mass differences for the HEK293 data set and likely modifications sourced from Unimod corresponding to these precursor mass differences. The delta-mass column contains the median precursor mass difference of that SSM subgroup.

# SSMs	Δm (Da)	Potential modification
369 341	0.003
46 659	1.005	First isotopic peak
31473	15.998	Oxidation or hydroxylation / Ala → Ser substitution / Phe → Tyr substitution
14 088	2.006	Second isotopic peak
6 418	−0.991	Amidation
5 777	−17.023	Pyro-glu from Q / loss of ammonia
5 433	17.002	Replacement of proton with ammonium ion
4815	183.039	Aminoethylbenzenesulfonylation
4 777	27.998	Formylation / Ser → Asp substitution / Thr → Glu substitution
3 266	301.991	Unidentified modification [15, 40]