Although such analyses typically assume that a protein's peptide fragments are observed with equal likelihood, only a few so-called 'proteotypic' peptides are repeatedly and consistently identiﬁed for any given protein present in a mixture.
Others use it to refer to peptides which uniquely identify a protein among a larger set (usually an organism). Example:
We propose that the datum for proteome scoring should be a proteotypic peptide â€” that is, an experimentally observable peptide that uniquely identifies a specific protein or protein isoform.
Still others use it to mean both simultaneously. Example:
An essential step of any targeted analysis is determining which peptides are most representative and most likely to be observed for a protein of interest. These peptides are commonly referred to as proteotypic peptides and can be used as a suitable proxy for the protein.
What do you think? Vote how you most frequently hear the term "proteotypic peptide" used and comment any details or how you think the situation should be resolved.