Figure 1.

(A) ESI-MS spectra of peptide 18, dissolved in different solutions: (a) acetonitrile–water mixture containing 0.1% HCOOH; (b) D₂O; (c) D₂O containing 1% Et₃N; (d) acetonitrile–water mixture containing 0.1% HCOOH, after lyophilization from D₂O containing 1% Et₃N; (e) H₂O containing 1% Et₃N, after lyophilization from acetonitrile–water mixture containing 0.1% HCOOH. (B) ESI-MS/MS analysis of the respective ions