Hi, I am working on a practical involving protein digestion and I am confused as to how there can be a -19 Da difference. I believe it has something to do with the trypsin digestion and its accuracy, but I would like some clarification on the mechanisms of this. I am interested to hear people's thoughts on this.
The following three peptides are detected in the mass spectrometer with the masses listed.
Note that in each case the detected mass is 1 Da higher than the mass of the uncharged peptide because the form detected in the mass spectrometer is the protonated form (M+H+ ) and the mass of a hydrogen atom is 1 Da.
Peptide X: VVFAGAK: (M+H+ ) = 691.4 Da
Peptide Y: SQTTYAYR: (M+H+ ) = 989.5 Da
Peptide Z: VVFAGAKSQTTYAYR: (M+H+ ) = 1661.9 Da
The mass of peptide Z is the sum of the masses of peptides X and Y minus 19 Da.
What causes this -19 Da change.?
Dear Leon Matt ,
The m/z value of a peptide [M+H]+ is the sum of the residue masses plus 18.015 for H2O plus 1.008 because of a charge.
Sounds right what Michitoshi Watanabe wrote.
Dear Leon Matt ,
The m/z value of a peptide [M+H]+ is the sum of the residue masses plus 18.015 for H2O plus 1.008 because of a charge.
Sounds right what Michitoshi Watanabe wrote.
Tthree is adition of one water molecule due to hydrolysis of peptide Z
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