Question: A lysate was prepared from a mouse-derived cell line. Following digestion, LC-MS/MS analysis show…

A lysate was prepared from a mouse-derived cell line. Following
digestion, LC-MS/MS analysis showed strong signals from the
following peptides: YEELQITAGR and LGEHNIDVLEGNEQFINAAK. However,
neither of these peptides could be found in a database of proteins
from the mouse proteome. Why?