Peptide mapping of proteins in gel bands after partial cleavage with acidic cyanogen bromide vapors

A procedure is described for obtaining peptide maps from microgram quantities of protein in gel bands, after cleavage at the methionyl peptide bonds with vapors of acidic cyanogen bromide (CNBr). Absence of direct contact of the gel pieces with CNBr eliminates the need for extensive equilibration of the gel piece to remove CNBr prior to electrophoresis. The milder conditions lead to partial cleavage of the proteins, yielding larger peptides and thereby reducing the risk of peptide loss during the postelectrophoresis procedures. The "fingerprints" obtained are reproducible and independent of an eightfold change in CNBr concentration.