Place the cell culture dish on ice and wash the cells with ice-cold PBS.
Aspirate the PBS, then add ice-cold lysis buffer (1 mL per 107 cells/100 mm dish/150 cm2 flask; 0.5 mL per 5×106 cells/60 mm dish/75 cm2 flask).
Scrape adherent cells off the dish using a cold plastic cell scraper, then gently transfer the cell suspension into a pre-cooled microcentrifuge tube. Alternatively, cells can be trypsinized and washed with PBS prior to resuspension in lysis buffer in a microcentrifuge tube.
Maintain constant agitation for 30 min at 4°C.
Centrifuge the cell suspension in a microcentrifuge at 4°C. You may have to vary the centrifugation force and time depending on the cell type; a guideline is 5 min at 14,000-17,000 g but this must be determined for your experiment (leukocytes need very light centrifugation).
Gently remove the tubes from the centrifuge and place on ice, aspirate the supernatant and place in a fresh tube kept on ice, and discard the pellet.
Preparation of lysate from tissues
Dissect the tissue of interest with clean tools, on ice preferably, and as quickly as possible to prevent degradation by proteases.
Place the tissue in round-bottom microcentrifuge tubes or Eppendorf tubes and immerse in liquid nitrogen to snap freeze. Store samples at -80°C for later use or keep on ice for immediate homogenization. For a ~5 mg piece of tissue, add ~300 μL of ice-cold lysis buffer rapidly to the tube, homogenize with an electric homogenizer, rinse the blade twice with another 2 x 200 μL lysis buffer, then maintain constant agitation for 2 h at 4°C (eg place on an orbital shaker in the fridge). Volumes of lysis buffer must be determined in relation to the amount of tissue present; protein extract should not be too dilute to avoid loss of protein and large volumes of samples to be loaded onto gels. The minimum concentration is 0.1 mg/mL, optimal concentration is 1-5 mg/mL.
Centrifuge for 5-10 min at 14,000-17,000 g at 4°C in a microcentrifuge. Gently remove the tubes from the centrifuge and place on ice, aspirate the supernatant, and place in a fresh tube kept on ice; discard the pellet.
Sample preparation
Remove a small volume of lysate to perform a protein quantification assay. Determine the protein concentration for each cell lysate.
Determine how much protein to load and add an equal volume 2X Laemmli sample buffer.We recommend reducing and denaturing the samples using the following method unless the online antibody datasheet indicates that non-reducing and non-denaturing conditions should be used.
To reduce and denature your samples, boil each cell lysate in sample buffer at 100°C for 5 min. Lysates can be aliquoted and stored at -20°C for future use.
Loading and running the gel
Transferring the protein from the gel to the membrane
The membrane can be either nitrocellulose or PVDF. Activate PVDF with methanol for 1 min and rinse with transfer buffer before preparing the stack. The time and voltage of transfer may require some optimization. We recommend following the manufacturer’s instructions. Transfer of proteins to the membrane can be checked using Ponceau S staining before the blocking step.
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