Figure 2.

(A) Proteasome species found in different cell types. Extracts of HeLa cell (30 μg), rat cortex (60 μg), rat liver (40 μg) and rat kidney (50 μg) were resolved by 2–5% gradient native gel, immunoblotted against 19S subunit Rpt1, and reprobed against 20S subunit α7. Protein bands were pseudo-colored and merged to illustrate the presence of proteasomes and related species (from top to bottom): doubly-capped 26S proteasome, singly-capped 26S proteasome, free 19S particle and free 20S particle. A fast-migrating band corresponding to a subcomplex of the 19S containing Rpt1 protein was also observed. (B) The distribution of different proteasome species in (A), quantified by densitometry (mean ± SEM, n = 6). The experiment was performed independently six times with tissues from three animals. By one-way ANOVA and Turkey's multiple comparison test, doubly-capped 26S levels in cortex are found to be significantly higher (p < 0.01) than those in liver, kidney or HeLa cells.