Figure 4

Laser-induced modification of human serum albumin (HSA) peptide standard and insulin. Orbitrap ESI-FTMS mass spectra of laser-induced formylation of HSA standard peptides (A) LVNEVTEFAK, (B) AVMoxDDFAAFVEK, and (C) KVPQVSTPTLVEVSR. Laser-induced formylation of human insulin (D) was also observed. The unmodified forms of the peptides and insulin correspond to the first labeled peak in each mass spectrum. The charge state of each peptide or protein observed by electrospray ionization is indicated below the m/z value. The modified forms have a net addition of CO (+28 Da). In all cases, modification was conducted in ACN:water (98:2; % v/v), at room temperature in air by 300,000 laser pulses at wavelength 386 nm with average pulse energy 269.5 μJ at intensity 5.19 × 10¹⁰ W cm⁻².