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#Da shift

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

A shift of 98 Da less than expected in MS/MS means:

Phosphorylation adds 80 Da, but under collision-induced dissociation phosphorylated serine and threonine frequently undergo beta-elimination of phosphoric acid H3PO4 with mass 97.9769 Da, rounded to 98 Da loss from precursor or product ions. Observation of peak 98 Da lower than predicted molecular weight signals neutral loss of phosphate, indicating presence of phosphopeptide that lost H3PO4 during fragmentation. This diagnostic loss distinguishes phosphorylated peptides from unmodified counterparts and contrasts with oxidation or deamination shifts. Recognition of -98 Da loss supports phosphosite localization in signal transduction studies and proteomics research widely used.

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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