were characterized
by mass spectrometry on a Bruker Daltonics UltrafleXtreme matrix-assisted
desorption ionization time-of-flight mass spectrometer operating in
positive-ion reflector mode [matrix of α-cyano-4-hydroxycinnamic
acid (CHCA), external calibration]. High-resolution mass spectrometry
was performed on a Waters Synapt G2-S nano-ESI-IMS-TOF mass spectrometer.
Analytical HPLC measurements were performed using a JASCO chromatography
system and a Phenomenex Prodigy ODS-3 column (5 μm, 4.6 mm ×
100 mm). For peptide characterization, a linear gradient of water
and acetonitrile (buffer A consisted of water and 0.1% TFA, and buffer
B consisted of acetonitrile and 0.1% TFA) run from 20 to 80% over
20 min was used. Chromatograms were monitored at wavelengths of 220
and 280 nm.