Hope this answer will help you:
To know the sequence of amino acid, the best way is to cut
the target protein with some enzymes. Each enzyme has some cleavage site, after
what these enzymes cut the proteins into fragments with the help of amino
acids. However, when protein is cut with different enzymes, there will be
stretches of amino acids. There will become a proper sequence where fragments
are aligned together to produce the set of whole protein.