Proteomics and peptidomics: different scopes

In digestion-based proteomics, the resulting peptides are used to investigate their parent proteins. FASP exemplifies this strategy: it combines protein processing and digestion, followed by peptide recovery for analysis.

In this context, detecting a peptide does not mean it was free in the original material. Its presence may be a deliberate consequence of analytical preparation. A table of digestion fragments is therefore not automatically an inventory of the endogenous peptidome. Primary study.

An early study examined neuropeptides directly in cockroach neuroendocrine tissue by mass spectrometry. Some signals yielded complete sequences, while others provided only partial information.

This example shows two distinct limits: detecting a peptide signal does not ensure full structural resolution, and fragmentation data do not eliminate reference-database limitations. The result belongs to that tissue and platform rather than representing every peptide in the organism. Primary study.

A study of mouse liver and pancreas compared sampling procedures and observed differences in degradation products and endogenous peptides. The evaluation included both proteome and peptidome.

The lesson concerns attribution: a fragment found at the end may reflect processes after sampling rather than only the living tissue’s state. The study does not provide a universal preservation rule; it demonstrates sensitivity to preparation in the tissues and conditions examined. Primary study.

If the analysis uses fragments to infer proteins, the conclusion should explain that relationship. If it examines peptides present before deliberate digestion, retaining supported information about termini, modifications and specific assignments matters.

Two signals from one protein are not necessarily independent observations of its abundance. They may represent fragments, processed forms or shared assignments. Before combining them under one name, examine the transformations connecting the original sample to the table.

Coverage depends on preparation, separation, acquisition and identification criteria. The term global describes a broad strategy, but does not demonstrate that every possible molecule was observed.

Comparing studies is more informative when the interrogated fraction and unresolved information are stated. Absence from a table may reflect analytical scope. Likewise, identifying an endogenous peptide does not establish a signaling function by itself: identity and activity require different evidence.