Table 1. Oxidation of methionines.

Methionine-containing peptide fragments detected that show a mass increase of 16 or 32 Da after proteolytic digestion of TmPOx (inactivated during turnover of 100 mM D-glucose, treated with endogenous H₂O₂ or unaffected). Proteolytic digestion was performed with trypsin or Asp-N protease as indicated. The last column indicates whether the particular Met is considerably oxidised during substrate turnover and by H₂O₂ treatment compared to the unaffected sample (see also Fig 2).

Digestion	Peptide MH+ ion	Amino acids	Met position	Sequence	Oxidation
Trypsin	887.5	39–46	43	KVPGMDIK	Yes
Asp-N	1284.6	64–75	74	ELVGAGYKVAMF	No
Trypsin	1494.7	72–85	74	VAMFDIGEIDSGLK	No
Trypsin	722.4	378–383	380	SDMTIR	No
Asp-N	2894.4	379–405	380	DMTIRGTPGELTYSVTYTPGASTNKHP	No
Asp-N	2139.9	406–421	416, 417	DWWNEKVKNHMMQHQE	Yes, Yes
Trypsin	1815.8	491–505	497	ITDAYNMPQPTFDFR	Yes
Asp-N	1720.9	542–557	555	EPGLVLHLGGTHRMGF	Yes