Figure 3.

Characterization of purified [L91D,L-O]RBD/H, the artificial protein with N¹-methyl-7-azatryptophan as a racemate at position 91 and a C-terminal His tag. (a) Chromatogram after purification on a preparative C4 RP-HPLC column. The chromatogram was obtained on an analytical C4 RP-HPLC column with a gradient of 5–65% acetonitrile in H₂O, 0.1% trifluoroacetic acid over 30 min. (b) Electrospray ionization-mass spectrometry of the purified product with the 5H⁺–11H⁺ charged states of the polypeptide corresponding to a measured mass of 10,544.5 ± 1.1 Da (calculated mass with an average isotope composition: 10,544.1 Da).