Table 2.

Identification of cysteine-containing peptides from oxidized PKG Iα

Cysteine	Sequence with modificationsa	z+	Theoretical m/z (monoisotopic)	Observed m/z (monoisotopic)	Concentration	Retention time
					ppm	min
Cys-42	K↓C@QSVLPVPSTHIGPR↓T	2	819.917	819.917	0.00	37.88
	K↓C#QSVLPVPSTHIGPR↓T	2	811.920	811.921	1.23	37.96
	K↓C⋀QSVLPVPSTHIGPR↓T	2	824.435	824.437	2.42	34.34
	K↓C∼QSVLPVPSTHIGPR↓T	2	844.433	844.435	2.37	40.13
Cys-117	K↓NLELSQIQEIVDC@M*YPVEYGK↓D	3	845.726	845.724	−2.36	58.92
	K↓NLELSQIQEIVDC⋀M*YPVEYGK↓D	3	848.738	848.739	1.17	58.25
	K↓NLELSQIQEIVDC∼M*YPVEYGK↓D	3	862.070	862.069	1.15	58.89
Cys-195	R↓QC∼FQTIMMR↓T	2	627.775	627.776	1.59	24.48
	R↓QC∼FQTIM*MR↓T	2	635.773	635.772	1.57	30.43
	R↓QC∼FQTIM*M*R↓T	2	643.770	643.771	1.55	34.03

^a Modifications were as follows: *, oxidation; #, sulfinic acid; @, sulfonic acid; ⋀, iodoacetamide (free thiol, previously disulfide-bound); ∼, maleimide (free thiol).