You have isolated the proteins from two other adjacent spots after 2D electropho

Question

You have isolated the proteins from two other adjacent spots after 2D electrophoresis and digested them with trypsin. Following MALDI-TOF mass spectrometry, the 2 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 i instead of valine at one position would give an m/2 difference of around 30.) Can you suggest a possible difference between the two peptides that might account for the observed m/z difference? m/z (mass to chare ratio)

Explanation / Answer

Answer:

The Glycine residue has molecular weight = 57.0513 and the Histidine residue has molecular weight = 137.1393

So the difference in molecular weight = 137.1393 - 57.0513 = 80.088

So the possible difference of mass -to-charge ratio (m/z) in a the above one peak is might be the histidine instead of glycine in one position for which the difference in m/z is around 80.

*The residue means after removal of water molecule from aminoacid.

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