The principle behind peptide mass fingerprint for protein identification is that a mixture of peptides unique to that protein will be generated after the protein being digested by a specific enzyme. The characteristic dataset of the molecular masses of these digested peptides called a peptide mass fingerprint (PMF). By comparing with theoretical peptide molecular masses dataset that can be generated by using the same protease to digest each protein in the sequence database, the best match can be find out. PMF identification relies on observing a large number of peptides, at least 5 peptides from the same protein with high accuracy.