Peptide sequence information derived by Pronase Digestion and ammonium sulfate in-source decay matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We present the use of Pronase digestion and in-source decay in the presence of ammonium sulfate as complementary techniques to confirm the amino acid sequence of a peptide. Pronase, a commercial preparation from Steptomyces g riseus, is a combination of proteolytic enzymes. It produces carboxypeptida se and aminopeptidase ladders using a single Pronase digestion and represen ts an inexpensive, nonspecific, and fast supplement to traditional sequenci ng enzymes. However, N-terminal peptidase activity appears dependent on the terminal amino acid residue. We also introduce the use of saturated ammoni um sulfate as an "on-slide" sample additive to promote in-source fragmentat ion of peptides. Use of saturated ammonium sulfate resulted in a simple way to increase peptide backbone fragmentation and essentially produced either a c(n) or y(n) ion series. Together these techniques provide useful supple ments to existing methods for peptide sequence information, (C) 2000 Americ an Society for Mass Spectrometry.