Progress in plasma desorption mass spectrometry of peptides and proteins.

The principles and some applications of plasma desorption (PD) m.s. were described in this Journal in a report from the Biochemical Society's 618th Meeting in Liverpool on 2-4 April 1986 (Roepstorff et al., 1 9 8 7 ~ ) . Since then, PD-m.s. has developed to become a routine method in protein studies in our laboratory. During this period the sample preparation techniques using adsorption to nitrocellulose (Jonsson et al., 1986) have been improved, resulting in an increased sensitivity and extended applicability. The largest protein for which molecular ions had been seen was at that time trypsin ( M , 23 406). Since then molecular ions have been observed for larger proteins, e.g. subtilisin, carbonic anhydrase and the hitherto largest protein observed in the gas phase, porcine pepsin, for which the M , was measured at 34 630 (Craig et ul., 1987). Thc present report describes thc improvements of the technique which have been obtained as a result of the collaboration between our laboratory and Dr B. Sundqvist and collaborators at the Tandem Accelerator Laboratory, Uppsala University, Uppsala, Sweden. Furthermore, it describes recent applications of PD-m.s. to protein studies in our laboratory and outlines general strategies for the use of PD-m.s. in protein sequence studics and biotechnology. For a more extensive survey of PD-m.s., see the recent reviews by Sundqvist & Macfarlane ( 1985) and Roepstorff & Sundqvist (1986).