Uses of DTT (dithiothreitol) in proteomics and SDS-PAGE sample preparation

What is DTT and why is it used in SDS-PAGE?

Dithiothreitol (DTT, CAS 3483-12-3) is a small-molecule reducing agent widely used in protein biochemistry. In SDS-PAGE sample preparation, DTT is added to disrupt disulphide bonds (S–S) within and between polypeptide chains. This ensures complete denaturation of proteins, allowing them to migrate based on molecular weight rather than tertiary structure. Without reduction, proteins may remain partially folded or aggregated, leading to smearing or inconsistent banding patterns on gels. DTT is typically used at final concentrations of 1–5 mM in sample buffer, depending on the protein’s disulphide content and stability requirements.

How does DTT compare to other reducing agents?

DTT is preferred over β-mercaptoethanol (BME) in most modern protocols due to its higher reducing power (E⁰ = −0.33 V vs. −0.37 V for BME), lower volatility, and reduced odour. Unlike BME, DTT does not degrade significantly in aqueous solution at room temperature, maintaining stability for several weeks when stored at −20 °C. However, DTT is less stable in alkaline conditions and can oxidise over time, especially in the presence of oxygen. For this reason, fresh preparation or storage under inert gas is recommended. In contrast, BME is more stable in alkaline buffers but has a strong, unpleasant odour and is more prone to oxidation. DTT is also compatible with mass spectrometry workflows, as it does not interfere with ionisation or adduct formation as readily as some other reductants.

What concentration of DTT should be used in sample preparation?

The standard concentration of DTT in SDS-PAGE sample buffer is 1–5 mM. For most routine applications, 2–3 mM is sufficient to reduce common disulphide bonds in serum proteins, enzymes, and membrane proteins. For proteins with multiple or highly stable disulphide bonds (e.g., IgG, ribonuclease A), concentrations up to 5 mM may be required. Higher concentrations (>5 mM) are generally avoided due to potential interference with downstream assays, such as ELISA or mass spectrometry, and increased risk of non-specific reduction. The exact concentration may depend on the protein’s isoform, buffer composition, and incubation time. For example, a 5-minute incubation at 95 °C with 1 mM DTT is often sufficient for standard denaturation, while prolonged heating (10–15 min) may allow lower concentrations to be effective.

Can DTT be used in proteomics workflows beyond SDS-PAGE?

Yes, DTT is extensively used in proteomics workflows beyond SDS-PAGE. In bottom-up proteomics, DTT is employed during protein digestion to reduce disulphide bonds prior to tryptic cleavage. This ensures complete access of proteases to cleavage sites and improves peptide recovery and identification. DTT is also used in sample preparation for mass spectrometry (MS), particularly in label-free and TMT-based quantification. However, DTT can interfere with cysteine alkylation steps, which are critical for preventing re-oxidation of reduced cysteines. Therefore, DTT is typically removed or quenched with iodoacetamide (IAA) or N-ethylmaleimide (NEM) after reduction. The use of DTT in combination with alkylation is standard in most proteomic pipelines, including those involving LC-MS/MS analysis.

What are the stability and handling considerations for DTT?

DTT is hygroscopic and sensitive to oxidation. It should be stored at −20 °C in airtight containers to minimise exposure to moisture and oxygen. Solutions of DTT are best prepared fresh and used within 24–48 hours to avoid degradation. Oxidised DTT forms a disulphide dimer (DTT-SS-DTT), which is ineffective as a reducing agent. The presence of oxidised DTT can be monitored by UV absorbance at 260 nm (oxidised form has higher absorbance) or by HPLC. For long-term storage, DTT is often supplied as a solid powder with a Certificate of Analysis (CoA) confirming purity (typically ≥98% by HPLC). It is also important to note that DTT is not regulated under REACH or TSCA, but it is classified under GHS as a skin and eye irritant (H315, H314), requiring appropriate handling precautions.

Sources

• Sigma-Aldrich: Dithiothreitol (CAS 3483-12-3)
• Thermo Fisher Scientific: DTT Technical Data Sheet
• NCBI: DTT in Protein Reduction and Mass Spectrometry
• Proteomics Protocols: Sample Preparation for LC-MS/MS
• European Chemicals Agency: REACH Registration

Frequently asked

• What is the typical concentration of DTT in SDS-PAGE sample buffer? 1–5 mM, commonly 2–3 mM for standard applications.

• Can DTT be used in mass spectrometry sample preparation? Yes, but it must be followed by alkylation (e.g., with iodoacetamide) to prevent re-oxidation.

• How should DTT be stored? At −20 °C in airtight, moisture-proof containers to prevent oxidation.

• Is DTT safer than β-mercaptoethanol? Yes, DTT has lower volatility and odour, and is less irritating to skin and eyes when handled properly.