Stable Isotope Labeling Service for Proteins & Peptides

Stable isotope-labeled proteins and peptides are essential tools in modern molecular research, yet preparing them is often slow and technically demanding. Growing cells in labeled media, expressing and purifying a target, or chemically synthesizing a labeled peptide with the right enrichment all require specialized know-how that a typical biochemistry lab may not have on hand. Beyond the benchwork, the hidden costs are time and uncertainty: a mis-targeted enrichment level, a low-purity prep, or an inconsistent batch can waste weeks of downstream instrument time. Our labeling service delivers enrichment-verified material with documented purity, so your team can move straight to the experiment instead of re-optimizing the supply chain.

Labeled samples underpin work that unlabeled material cannot: resolving protein structures and dynamics by nuclear magnetic resonance, quantifying and tracing molecules by mass spectrometry, and following metabolic flux through living systems. Supplying the labeled building blocks reliably is therefore the first step in many structural and quantitative studies. Because the optimal labeling pattern depends heavily on the intended readout, we begin each project with a short planning discussion rather than a one-size-fits-all protocol — the same protein may need uniform labeling for a structure, residue-selective labeling for an interaction study, or partial labeling to reduce spectral overlap. Matching the strategy to the experiment is what turns a labeled sample from a reagent into a result.

Researchers commonly turn to a dedicated labeling partner when an in-house attempt has stalled, when instrument and staff time are better spent on measurement than on production, or when a study needs reproducible material across several batches. Whether the goal is a single high-quality construct or a series of peptide standards, the work packages below describe what we deliver and how it is verified before it reaches your bench.

What the Service Covers

• 13C labeling – uniform or site-specific carbon labeling for NMR and mass-based readouts.
• 15N labeling – nitrogen labeling commonly paired with 13C for heteronuclear NMR.
• Proteins – recombinant expression in labeled media with purification to research grade.
• Peptides – labeled residues incorporated during chemical synthesis to a defined pattern.

Typical Approaches

Labeling Strategy

The first design decision is whether the label should be distributed across the whole molecule or placed at specific positions. Each choice trades information against effort, and the right answer follows directly from the experiment you intend to run.

• Uniform labeling – the isotope is incorporated throughout the molecule during expression or synthesis. This gives the strongest, most complete signal for heteronuclear NMR and for global tracing studies, and is usually the most economical route when the entire sequence needs to be observed.
• Site-specific / residue-selective labeling – the label is placed only at chosen residues or domains. This reduces spectral overlap in crowded regions, lets you isolate a single interaction site, and is valuable when only part of a protein carries the signal you care about. It is more demanding to produce and is typically applied to peptides or to proteins where uniform labeling would obscure the readout.
• Partial or fractional labeling – an intermediate pattern used to simplify complex spectra by lowering the probability that adjacent nuclei are both labeled. This is a specialized option we discuss when uniform labeling produces unresolved data.

Where the boundary falls depends on construct size, the available assignment, and the instrumentation. We recommend a pattern during the strategy consult and explain the trade-off in plain terms so the choice is deliberate rather than accidental.

How to Choose Isotopes

Most projects use one or two of the common stable isotopes. The table below is a practical starting point; the final selection is matched to your detection method and the questions you are asking.

If your method is mass-spectrometry based rather than NMR, the deciding factor is usually the mass separation you need between labeled and unlabeled species, which governs how much enrichment is required to keep quantification clean. We set the enrichment target with that separation in mind.

Workflow

• Strategy consult – define isotope(s), enrichment level, and target application.
• Production – labeled expression or synthesis according to the agreed design.
• Purification – isolate the product to the required purity.
• Verification – confirm isotope enrichment and identity before release.
• Delivery – ship material with documentation of enrichment and purity.

Applications

• Structural biology – NMR-based protein structure, dynamics, and interaction mapping. Labeled proteins supply the resolved signals needed for backbone and side-chain assignment, for measuring motions on multiple timescales, and for mapping binding interfaces where only the labeled partner is observed. Larger systems benefit from combined 2H/13C/15N schemes that keep spectra readable.
• Mass spectrometry – quantitative proteomics and metabolite tracing. A known mass shift lets you mix labeled and unlabeled samples and read relative abundance directly, which underpins spike-in standards, absolute quantification, and isotope-dilution workflows. For peptides, defined labeling patterns serve as internal standards that correct for recovery and ionization differences.
• Metabolic research – flux and pathway analysis using labeled tracers. Feeding labeled substrates and reading where the isotope appears reveals pathway activity and nutrient routing in cells or organisms, and the same material supports turnover and kinetic studies where the rate of label appearance or loss is the measurement.
• Method development – labeled references are used to calibrate instruments, validate new assays, and train computational pipelines where a ground-truth signal is required.

Why Outsource Labeling

Labeling, expression, and purification together form a long, failure-prone chain. Outsourcing reduces cycle time, frees instrument and staff capacity, and returns material with verified enrichment so downstream experiments start from a known state.