Preparation of Modifed Radioimmunoprecipitation (RIPA) Buffer
RIPA Base Ingredients
- Tris-HCl (buffering agent prevents protein denaturation)
- NaCl (salt prevents non-specific protein aggregation)
- NP-40 (non-ionic detergent to extract proteins; 10% stock solution in H20)
- Na-deoxycholate (ionic detergent to extract proteins; 10% stock solution in H2O; protect from light)
[Note: Do not add Na-deoxycholate when preparing lysates for kinase assays. Ionic detergents can denature proteins, causing them to lose activity.]
RIPA Protease Inhibitors
- Phenylmethylsulfonyl fluoride (PMSF) (200 mM stock solution in isopropanol; store at room temperature)
- EDTA (calcium chelator; 100 mM stock solution in H2O, pH 7.4)
- Leupeptin (store frozen in aliquots, 1 mg/ml in H2O)
- Aprotinin (store frozen in aliquots, 1 mg/ml in H2O)
- Pepstatin (store frozen in aliquots, 1 mg/ml in methanol)
RIPA Phosphatase Inhibitors
[Note: Do not add phosphatase inhibitors when preparing lysates for phosphatase assays.]
Prepare 100 ml modified RIPA buffer as follows:
1. Add 790 mg Tris base to 75 ml distilled H2O. Add 900 mg NaCl and stir the solution until all solids are dissolved. Using HCl, adjust the pH to 7.4.
2. Add 10 ml of 10% NP-40 to the solution.
3. Add 2.5 ml of 10% Na-deoxycholate and stir until solution is clear.
4. Add 1 ml of 100 mM EDTA to the solution. Adjust the volume of the solution to 100 ml using a graduated cylinder. Store RIPA buffer at 2-8íC until ready to use.
5. Ideally, the remaining protease and phosphatase inhibitors should be added to the solution on the same day the assay is run (100 microliters of aprotinin, leupeptin, and pepstatin; 500 microliters of PMSF, Na3VO4, and NaF), but with the exception of PMSF the diluted inhibitors are stable in aqueous solution for up to 5 days. PMSF is extremely unstable in aqueous solutions with a half-life of approximately 30 minutes and should be added immediately before use.
The final concentrations in the modified RIPA buffer should be:
- Tris-HCl: 50 mM, pH 7.4
- NP-40: 1%
- Na-deoxycholate: 0.25%
- NaCl: 150 mM
- EDTA: 1 mM
- PMSF: 1 mM
- Aprotinin, leupeptin, pepstatin: 1 microgram/ml each
- Na3VO4: 1 mM
- NaF: 1 mM