assignment to each region of the molecule (тема: Пептидное картирование)

[Mishonok]

Помогите, пожалуйста, с переводом отрывка:

Peptide mapping. Tryptic digestion and RP-HPLC analysis of IFN-alfa 2b are shown in Figure 4. The chromatogram obtained is the same as previously reported [21]. Nevertheless, sequence verification by mass spectrometry was performed on every peak observed in the map. Mass values were determined, and assignment to each region of the molecule was done [21]. The peptides identified by m/z 1313.6 (peaks 13 and 14), corresponding to the N-terminal region, confirmed the protein integrity at this end. These values also indicate the total absence of IFN-alfa 2b species with modified N-terminus.

Особенно не понятно:
- assignment to each region of the molecule was done
- N-terminal region / species with modified N-terminus

Заранее большое спасибо.