N-terminal sequence determination of polypeptides and peptide mixtures by Edman degradation combined with californium-252 plasma desorption mass spectrometry.

The combination of manual Edman degradation with 252Cf plasma desorption mass spectrometry has been developed as an efficient method of polypeptide sequence determination. Results obtained with a variety of peptides and small proteins demonstrate unequivocal, two-fold sequence data, at each step from molecular weight identification of successively truncated Edman coupling and cleavage products. A rapid, greatly simplified procedure of manual Edman degradation with phenyl isothiocyanate was employed without extraction and purification steps, which was found compatible with plasma desorption mass spectrometry of low picomole amounts of peptide sample, at each cycle. Particular advantages of this combined method are the possibility of obtaining simultaneous sequence information from multicomponent peptide mixtures, such as proteolytic digests, and the direct identification of modified sequences, such as glycosylation sites. With the currently used conditions, plasma desorption mass spectrometry has been found feasible for approximately 30 sequence steps and sensitive to subnanomole amounts of proteins, with Mr up to approximately 10,000 Da.