May I precipitate with TCA prior to loading to SDS gel?
Is it ok if I precipitate my samples with TCA prior to loading them to the SDS-Gel – to increase the protein concentration? If not, how do you recommend reducing the volume of my sample?
There are different methods to increase the protein concentration before loading onto a 1D gel, including dialysis, micro con type spin filters, precipitation, and chromatography [1, 2].
You can use TCA precipitation, but TCA is a very strong acid and may lead to hydrolysis and fragmentation of some proteins .
We often use ice-cold ethanol/acetone precipitation, because it increases the protein concentration and removes most salts and buffer components [1-3].
Briefly, the samples are mixed with ice-cold ethanol (100 ul:400 ul), incubated at -20°C. Subsequently, 400 ul ice-cold acetone is added and again incubated at -20°C. We then centrifuge the samples and wash them with acetone/ethanol/water (2:2:1) [2, 4].
Or use this classical “Acetone Precipitation Protocol” to increase protein concentration:
1. Cool the required volume of acetone to -20°C (we keep a bottle in the freezer).
2. Place the protein sample in an acetone-compatible tube. Test the tube before use, because some tubes dissolve in acetone!
3. Add four times the sample volume of cold (-20°C) acetone to the tube.
4. Mix the tube and incubate for 60 minutes at -20°C.
5. Centrifuge the tube for 10 minutes at 13,000-15,000 x g.
6. Decant and properly dispose of the supernatant. Be careful to not dislodge the protein pellet.
Optional: If additional cycles of precipitation are necessary to completely remove the interfering substance, then repeat steps 2-5 before proceeding to step 7.
7. Allow the acetone to evaporate from the uncapped tube at room temperature for 30 minutes. Do not over-dry the pellet and do not speedily vac dry for too long. The protein may not dissolve again but stay as a white pellet.
8. Finally, you should resuspend in an appropriate buffer.
Most samples can be redissolved in a 1D sample buffer that contains SDS.
Read more about protein separation by electrophoresis here.
 Posch, A.: “2D PAGE: Sample Preparation and Fractionation“, Methods in Molecular Biology, 2008
 Chen et al: “A modified protein precipitation procedure for efficient removal of albumin from serum“, Electrophoresis, 2005
 Koontz, L.: “Chapter One – TCA Precipitation“, Methods in Enzymology, 2014
 Zellner et al: “Quantitative validation of different protein precipitation methods in proteome analysis of blood platelets“, Electrophoresis, 2005