The observation of quasi-molecular ions from a protein neurotoxin (MW 7821) using 127I-plasma desorption mass spectroscopy

Fast heavy ions, i.e. 90 MeV ¹²⁷I from the Uppsala tandem accelerator have been used to desorb and ionize molecules from a cobra venom neurotoxin. The protein is built up by 71 amino acid residues in a single polypeptide chain, tightly cross-linked by 5 disulfide bridges. The molecular weight as confirmed by protein sequence analysis is 7821. The ions were mass analyzed by the time-of-flight technique. This is to our knowledge the largest protein for which it has been possible to detect quasimolecular ions by a mass spectrometric technique.