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. 2016 Apr 5;11(4):e0153002. doi: 10.1371/journal.pone.0153002

Fig 4. LC-ESI-MS/MS analysis of oxidized amino acids in the EGCG-treated HSA.

Fig 4

(A) Chemical structures of aminoadipic semialdehyde (AAS) and glutamic semialdehyde (GGS). (B) Collision-induced dissociation of the [M+H]+ of ABA-AAS at m/z 267 at a collision energy of 25 V and the proposed structures of individual ions. (C) Collision-induced dissociation of the [M+H]+ of ABA-GGS at m/z 253 at a collision energy of 25 V and the proposed structures of individual ions. (D) The ion current tracings of ABA-AAS (left three tracings) and ABA-GGS (right three tracings) using LC-ESI-MS/MS with SRM. (E) Determination of AAS in the EGCG-treated HSA. HSA (1 mg/ml) was incubated with EGCG (1 mM) in 0.1 ml of PBS (pH 7.4) for 24 h at 37°C. The yield of AAS was semi-quantitatively determined based on a calibration curve (S3 Fig). (F) Schematic illustration of the transformation of a lysine residue to AAS by EGCG.