Figure 4.

¹H–¹³C HSQC spectrum of the aromatic region of the Trp-containing peptide Ac–Gly–Gly–Trp–Gly–Gly–NH₂ under denaturing conditions (7 M urea-d₄ in D₂O) after treatment with 1% H₂O₂ for 5 h, dialysis, and lyophilization. Four different oxidation products of Trp could be detected and are shown on the right. For HPI, Oia, and NFK, two sets of shifts can be observed due to different stereoisomers.