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#peptide modification

3 public questions tagged with this topic.

Mass Spectroscopy

Which modification causes +28 Da shift?

Post-translational modifications exhibit characteristic mass increments in mass spectrometry analysis. Formylation introduces a formyl group –CHO to lysine or N-terminus through formyl phosphate donor or chemical artifact, adding CO moiety essentially 27.995 Da rounded to +28 Da to peptide mass. This shift must be distinguished from dimethylation or ethylation. Sulfonation adds 80 Da, methylation adds 14 Da, phosphorylation adds 80 Da. Detection of +28 Da suggests formylation event often observed as artifact in formaldehyde crosslinking or as biologically relevant histone modification influencing protein function assessed in high-resolution accurate-mass protein studies carefully evaluated today.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Mass Spectroscopy

Phosphorylation of a peptide increases mass by:

Protein phosphorylation adds HPO3 group to serine, threonine, or tyrosine hydroxyl residues through kinase activity, fundamentally regulating signaling pathways. In mass spectrometry, attachment of phosphate adds monoisotopic mass of 79.9663 Da, commonly rounded to +80 Da compared to unmodified peptide. This signature shift enables phosphopeptide enrichment identification using titanium dioxide and tandem mass spectrometry. Neutral loss of 98 Da corresponding to H3PO4 may also occur under collision-induced dissociation, providing diagnostic confirmation. Recognizing +80 Da allows mapping of regulatory sites in cell biology.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Mass Spectroscopy

What mass shift does oxidation of methionine cause?

Methionine contains a thioether side chain highly susceptible to oxidation during sample handling, electrophoresis, or in vivo oxidative stress conditions. Addition of a single oxygen atom to sulfur forms methionine sulfoxide, increasing monoisotopic mass by 15.9949 Da, rounded to +16 Da in low-resolution spectra. This mass increment is a common variable modification included in proteomics database searches. Detection of +16 Da shift at methionine residues helps monitor oxidative damage, aging of proteins, and artifactual modifications, distinguishing true biological regulation from sample preparation induced oxidation in mass spectrometry analysis.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details