Laemmli buffer: Preparation (1x,2x & 4x) and principle
Introduction
The Laemmli sample buffer / Laemmli buffer is used for the better isolation of proteins in SDS-PAGE gel electrophoresis. The buffer is connected with the invention of SDS-PAGE during the quest for finding T4 phase proteins and got its name after the inventor Prof. Ulrich K. Laemmli [1]. The composition has been discussed since the 70s and alternatives have been proposed. Nevertheless, the Laemmli-based solution is still used and sold by companies with minor differences.
Commonly used alternatives are
- Morris SDS-PAGE sample buffer (very similar composition) or
- Phosphate modification of Laemmli sample buffer
Phosphate modification of the Laemmli is known to reduce unexpected protein cleavage, thanks to the better-buffering capacity of phosphate at used pH [2].
Principle
Tris is a buffering substance. As discussed above, the tris buffering system and the pH play an essential role in preserving peptide bonds from breaking apart.
SDS: Proteins come in different sizes and charges. SDS helps linearize (by denaturing) the proteins and bringing a net negative charge to the proteins irrespective of the initial charge. This minimizes variations in variations in the movement of proteins in the gel otherwise skewed by the difference in charge and shape.
Glycerol: The high density (thickening of the solution) of glycerol ensures the sample moves down into the well.
Beta-mercaptoethanol: is used for breaking the disulfide bonds. Beta-mercaptoethanol, along with SDS, ensure the bands are due to individual polypeptides instead of molecular complexes.
Bromophenol blue: visually indicates the location (tracking dye) of the sample in the gel.
Although the reagents mentioned above are used in standard Laemmli buffer, variations of the buffer have other substitutes. The following table represents which reagent in the buffer is substituted with others.
Applications
- This buffer is used as a sample preparation buffer for protein samples in SDS-PAGE, compatible with Tris-glycine-SDS running buffer.
- It can be used for resuspension of Immunoprecipitation beads before SDS-PAGE.
Composition
The Laemmli buffer is often prepared as a 2X or 4X solution and is mixed with the sample to 1X.
Standard Laemmli sample buffer contains:
| Reagent | Molecular weight | Concentration (M or %) | Add for 50 ml of 2X | Add for 50 ml of 4X | ||
|---|---|---|---|---|---|---|
| 1X | 2X | 4X | ||||
| Tris base1 | 121.14 | 0.0625 M | 0.125 M | 0.250 M | 0.747 g | 1.514 g |
| SDS2 | 288.37 | 0.07 M (2%) | 0.14 M (4%) | 0.28 M (8%) | 2 g | 4 g |
| glycerol | 92.09 | 10% | 20% | 40% | 10 ml | 20 ml |
| 2-mercapto-ethanol | 78.13 | 5% | 10% | 20% | 5 ml | 10 ml |
| Bromphenol blue3 | 691.94 | - | - | - | 100 mg | 200 mg |
Table 1. Composition of Laemmli sample buffer.
1Tris base is tris (hydroxymethyl) aminomethane. You can avoid using crystalline Tris by using Tris buffer, adjusted with HCl to 6.8.
2SDS is sodium dodecyl sulfate.
3Bromphenol blue is available as sodium salt or solution. Some modern protocols are using higher concentration (0.005 % Bio-rad, 0.002 % Sigma-Aldrich) to obtain bright colour.
pH
pH 6.8 is used, although it is below the buffering capacity of Tris (pH 7-9). The nearly neutral pH is used because low pH causes the peptide bonds to hydrolyse and on the other hand, high pH disrupts the activity of thiols.
The pH is normally adjusted with HCl and NaOH.
Preparation
Procedure (50 ml):
- Prepare the Tris solution by dissolving the exact amount of Tris base in 10 ml of water in a beaker. Use magnetic stirrer if needed.
- Adjust the pH to 6.8 with concentrated HCl. Be careful not to overshoot.
- Add glycerol to the tris solution using a cylinder and mix well.
- Add the exact amount of SDS and bromphenol blue. It takes time to dissolve, stirrer recommended.
In the next step, you have two options for adding beta-mercaptoethanol:
Option 1:
- Add mercaptoethanol and adjust the total volume to 50 ml.
- Divide in aliquots.
- Store at -20 °C.
Option 2:
- Adjust the volume so you can add mercaptoethanol just before use (e. g. for 2X adjust to about 45 ml).
- Divide in aliquots and store.
- Add mercaptoethanol just before use.
Option 1 is for quick use, choose the second option for better results.
Storage
If any thiol was added, store at -20 °C or use quickly.
Without thiols, it can be stored at room temperature or at 4°C.
Points to be noted
- Concentrated HCl fumes are dangerous, use it in a fumigation hood.
- Mercaptoethanol is seriously irritating and toxic if swallowed or inhaled, so it is advised to handle it in an active fumigation hood.
- Tris base is a skin and eye irritant as well as bromphenol blue.