You have isolated the proteins from two other adjacent spots

You have isolated the proteins from two other adjacent spots after 2D electrophoresis and digested them with? trypsin. Following MALDI-TOF mass spectrometry, the two proteins were found to be identical except for one peak. For this peak, the mass-to-charge ratio (m/z) values differed by 80 g/mol (or Daltons), a value that does not correspond to any discrete difference in amino acid sequence. (For example, glutamic acid instead of valine at one position would give an m/z difference of around 30.) Can you suggest a possible difference between the two peptides that might account for the observed m/z difference?

Solution

If the mass to charge ratio value is differed by 80 g/mol will indicates more than two elements are involved and based on the study of MALDI-TOF studies on peptides/proteins indicates it contains Valine(V), Glycine(G) and Glutamate(E) are present in that protein gives that value