FIGURE 6.

MALDI-TOF mass spectra of wild-type and N52S/N74S/N84T mutant anti-hCG VHH with and without heat treatment. A, MALDI-TOF mass spectra of wild-type (red) and N52S/N74S/N84T mutant (black) VHH (5 μm). B and C, samples were subjected to 40 heating-cooling cycles (B) or continuous 1,600-min (m) incubation (C) in HBS-EP buffer. The heating temperature was 90 °C. The spectra of wild-type VHH are presented with an offset of 200 m/z for clarity. The arrows indicate hypothetical fragments resulting from digestion occurring at the C terminus of Asn residues. In all panels, wild-type and N52S/N74S/N84T mutant VHH are abbreviated as WT and Mutant, respectively.