Proteolytic activities of the purified 20 S proteasomes from the heart and liver. A, comparison of the proteolytic activities of the 20 S proteasomes in cytosolic fractions from the heart and liver. *, p < 0.05; n = 4. B, comparison of the inhibition of 20 S proteasome activities in cytosolic fractions from the heart and liver. *, p < 0.05; n = 4. Heart and liver cytosol fractions (25 μg each) were assayed for β1, β2, and β5 activities in the presence of 100–500 mm of fluorescent substrate. *, p < 0.05; n = 5. C, comparison of the proteolytic activities of the purified 20 S proteasomes from the heart and liver. *, p < 0.05; n = 4. D, comparison of the inhibition of purified 20 S proteasome activities from the heart and liver.