Determination of the amino acid sequence of cystine-containing peptides by tandem mass spectrometry.

A method has been developed for the determination of the amino-acid sequence of a cyclic peptide containing cystine. It is based on the reduction of the peptide in a reductive matrix prior to ionization by fast-atom bombardment. The amino-acid sequence of the resulting linear peptide is then determined by tandem mass spectrometry from the spectrum produced by the collision-induced decomposition of the [M + H]+ ion of the peptide.