Chemical Tagging

Metabolic incorporation of heavy isotopes into a proteome — as used in SILAC and SILAM workflows — is a widely adopted method for preparing internal standards or labelled controls. However, some organisms and biological systems are not amenable to metabolic incorporation.

In these cases, analytes can be selectively modified using chemical tagging strategies. Chemical tagging enables stable isotope incorporation after protein extraction and is compatible with a wide range of biological sample types.

Common examples include:

• Reductive amination (dimethyl labelling) of primary amines in proteins and peptides

• Hydrazide tagging of free N-linked glycans in proteomic samples

To support these workflows, Cambridge Isotope Laboratories Inc.  (CIL) offers a collection of stable isotope labelling reagents, including reductive methylation reagents and the INLIGHT® glycan tagging kit (Individuality Normalization when Labelling with Isotopic Glycan Hydrazide Tag), enabling 2-plex or 3-plex relative quantitation by mass spectrometry.

Each technique is described in more detail on its associated product page.

INLIGHT® was developed by David Muddiman and colleagues at North Carolina State University. The kit is designed for the relative quantification of enzymatically cleaved N-glycans in binary (case vs control) or multiplexed samples using mass spectrometry.

The INLIGHT® approach improves:

• Quantitative accuracy

• Reproducibility

• Normalisation across biological samples

This method is particularly valuable in glycomics and biomarker discovery workflows.

The dimethyl labelling technique uses a reagent mixture of cyanoborohydride and formaldehyde (available in both unlabeled and stable isotope-labelled forms) to tag primary amines in proteins and peptides.

Targets include:

• The N-terminus

• The ε-amino group of lysine residues

This chemical tagging strategy is widely used in quantitative proteomics because it is:

• Cost-effective

• Rapid and simple to perform

• Compatible with LC-MS workflows

• Suitable for multiplexed relative quantitation

Dimethyl labelling provides a flexible alternative to metabolic labelling approaches when working with complex biological samples.