Table 3.

Calculated values of deconvoluted and theoretical masses relative to the experiments shown in Figures S3, S4, and 5.

	Deconvoluted masses (Da)	Theoretical masses (Da) from the primary structure
Figure S3. Mass spectrometry analysis of different variants of GFP
	GFP1M[1Met]: 26686.12 Da GFP1M[1Aha]: 26682.16 Da GFP2M[2Met]: 26716.26 Da GFP2M[2Aha]: 26707.57 Da	GFP1M[1Met]: 26685.80 Da GFP1M[1Aha]: 26680.72 Da GFP2M[2Met]: 26715.88 Da GFP2M[2Aha]: 26705.73 Da

Figure S4. Mass spectrometry analysis of different variants of ECFP
ECFP‐C	ECFP‐C[5Met]: 27709.85 ECFP‐C[4Met]: 27577.97 ECFP‐C[3Aha‐2Met]: 27692.67 ECFP‐C[3Aha‐1Met]: 27561.77	ECFP‐C[5Met]: 27708.87 ECFP‐C[4Met]: 27577.68 ECFP‐C[3Aha‐2Met]: 27693.57 ECFP‐C[3Aha‐1Met]: 27562.38
ECFP‐N	ECFP‐N[6Met]: 28285.05 ECFP‐N[5Aha‐1Met]: 28260.07	ECFP‐N[6Met]: 28284.51 ECFP‐N[5Aha‐1Met]: 28259.01

Figure 5. Mass spectrometry analysis of different target proteins and their dOG‐conjugated variants
B*	B* [1Aha‐1Met]: 10247.53 B* [1Aha‐1Met]‐dOG: 10825.67 Da B* [2Aha]‐2dOG: 11394.95	B* [1Aha‐1Met]: 10249.91 B* [2Met]: 10254.98 B* [2Aha]: 10244.83 B* [1Aha‐1Met]‐dOG: 10824.19 B* [2Aha]‐2dOG: 11393.39
GFP	GFP2M [2Met]: 26715.28 GFP2M [1Aha‐1Met]‐dOG: 27285.07 GFP2M [2Aha]‐2dOG: 27854.79	GFP2M [2Met]: 26715.88 GFP2M [1Aha‐1Met]‐dOG: 27285.09 GFP2M [2Aha]‐2dOG: 27854.29