Table 1.

A list of common modifications with isobaric delta masses

Number	Modification	Delta mass (Da)	Composition	Alternative explanation
1	Amidation	−0.984016	HN O(−1)	D to N, E to Q
2	Deamidation	0.984016	H(−1) N(−1) O	N to D, Q to E
3	Methylation	14.01565	H(2) C	G to A, D to E, V to I/L, S to T, N to Q
4	Formylation	27.994915	C O	D to S, E to T
5	di-Methylation	28.0313	H(4) C(2)	Ethyl, A to V, C to M
6	S-nitrosylation	28.990164	H(−1)NO	V to Q
7	Sulfide	31.972071	S	V to M, A to C
8	Di-Oxidation	31.989829	O(2)	P to E
9	Acetylation	42.010565	H(2) C(2) O	S to E
10	Tri-Methylation	42.04695	H(6) C(3)	Propyl, A to L/I, G to V
11	Carbamylation	43.005814	HCNO	A to N
12	Carboxylation	43.989829	C O(2)	A to D
13	Propionylation	56.026215	H(4) C(3) O	Acrolein adduct
14	Carbamidomethylation	57.021464	H(3) C(2) N O	A to Q, G to N, addition of glycine
15	Carboxymethylation	58.005479	H(2) C(2) O(2)	A to E, G to D
16	Methylmalonylation	100.016044	H(4) C(4) O(3)	Succinylation
17	Ubiquitin remnant (di-Gly)	114.042927	H(6) C(4) N(2) O(2)	Double carbamidomethylation, addition of asparagine