Modified RIPA buffer (50mM Tris-HCl, pH 7.4, 1% NP40, 0.25% sodium deoxycholate, 150mM NaCl, 1mM EDTA, 1mM PMSF, 1mg/ml aprotinin, 1mg/ml leupeptin, 1mg/ml pepstatin, 1mM Na3VO4, 1mM NaF) and diluted with non-reducing sample buffer (31mM Tris-HCl, pH 6.8, 5% glycerol, 1% SDS, 0.002% bromphenol blue).