Identification of Disulfide-Containing Peptides by FAB-MS

The following methods have been developed in conjunction with FAB-MS analysis [6-8]. 

Comparative Peptide Mapping This procedure is used when the protein is cleaved with specific cleaving agents and the sequence of the protein is known. A simple molecular mass measurement of the peptides in a protein digest will identify the position of a disulfide bond in the protein. 

Reduction of Disulfide Bonds The disulfide-bridged peptides can also be identified by analyzing the protein digest before and after the dithiothreitol reduction of disulfide bonds. The peaks due to disulfide-containing peptides will disappear, and new peaks related to reduced peptides will appear. If the peptide 

For interchain-linked peptides, the molecular ions of both of the constituent chains will be observed  

In a variation of this procedure, an S—S bond in a peptide can be reduced in situ during prolonged ( 5 min) irradiation of the peptide-matrix (dithiothreitol) by the fast atom beam. 

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