The plasma desorption mass spectrometry method is used to determine the molecular weights of larger molecules than before, to determine the molecular weights of proteins and peptides in mixtures, and to monitor protein modification reactions. Proteins up to molecular weight 25,000 can now be studied with a mass spectrometric technique. Protein-peptide mixtures that could not be resolved with conventional techniques were successfully analyzed by this technique. The precision of the method is good enough to permit one to follow the different steps in the conversion of porcine insulin to human insulin.

Animals↗

PubMed1984

Californium-252 plasma desorption time of flight mass spectroscopy of proteins.

Fast heavy ions, i.e. fission fragments from a 252Cf-source, have been used to desorb and ionize peptides and proteins from a sample surface. Masses of the desorbed ions have been determined by the time-of-flight technique. The mass interval of the molecules studied is 1000-14 000 u. Quasi-molecular ions of higher masses than earlier reported have been observed. The results include the detection of quasi-molecular ions of proinsulins, cytochrome-C, ribonuclease and two phospholipases. The general features of mass spectra of proteins using this ionization method are described. Emphasis is put on the discussion of metastable ion decay, neutral components, multiply charged ions, isotopic broadening, and cluster ion formation. Also the precision which can be obtained with a straight time-of-flight mass spectrometer will be discussed. Future applications of the technique are outlined.

Animals↗

PubMed1983

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 quasi-molecular ions by a mass spectrometric technique.

Amino Acid Sequence↗

PubMed1974

A fast method for nitrogen determination in single seeds.

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Nitrogen↗