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#mass shift

3 public questions tagged with this topic.

Mass Spectroscopy

A mass shift of +203 Da suggests presence of:

Glycosylation adds monosaccharide residues with defined masses to proteins, altering function and stability. N-acetyl glucosamine, GlcNAc, exists as common modification in N-linked and O-linked glycans and O-GlcNAc signaling. Residue mass of HexNAc after dehydration during glycosidic bond formation is 203.079 Da, observed as +203 Da increment on peptide mass spectra. Detecting this shift indicates single GlcNAc attachment, distinct from 162 Da for hexose, 146 Da for fucose, or 291 Da for sialic acid. Recognition of +203 Da aids mapping of glycosylation sites in proteomics studies.

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

A shift of +42 Da in MS indicates:

Lysine residues undergo enzymatic acetylation where an acetyl group CH3CO replaces hydrogen on epsilon amino group, neutralizing positive charge and regulating chromatin structure and metabolism. Addition of C2H2O minus H corresponds to monoisotopic mass increment of 42.0106 Da, observed as +42 Da shift in mass spectra. Detecting this modification on peptides helps identify epigenetic regulatory marks and metabolic regulation. Differentiation from trimethylation which also adds ~42 Da requires high resolution or diagnostic fragment ions, but in typical low-resolution proteomics workflows +42 Da strongly suggests acetylation event on proteins.

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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X Ray, IR Spectroscopy

Which modification causes a +16 Da shift in MS?

A mass increase of 16 daltons corresponds to addition of a single oxygen atom, atomic mass 15.995 Da. Methionine contains a sulfur thioether that is highly susceptible to reactive oxygen species, forming methionine sulfoxide with +16 Da shift and further oxidizing to sulfone with +32 Da. This artifactual or biologically relevant oxidation occurs during sample preparation, storage and oxidative stress, altering protein hydrophobicity and function. Acetylation adds C2H2O (+42 Da), carboxylation adds CO2 (+44 Da), and dehydration removes water (-18 Da), so oxidation uniquely explains the +16 signature commonly tracked in proteomics quality control.

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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