Table 1.

Inhibition of the proteasomal activity by lactacystin in OK cells

Lactacystin treatment	Inhibition (%)
0 μM (30 min)	0
1 μM (30 min)	64
10 μM (30 min)	83
50 μM (30 min)	97
0 μM (4.5 h)	0
1 μM (4.5 h)	82
10 μM (4.5 h)	>99
50 μM (4.5 h)	>99

Cells were incubated for 30 min or 4.5 h with different concentrations of the proteasomal inhibitor lactacystin. The cells were homogenized and centrifuged for 10 min at 16,000 × g in the cold, and the supernatants were assayed for proteasomal activity. Proteasomal peptidase activity was measured by monitoring the proteolysis of the fluorogenic proteasomal substrate succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin (28). The percent inhibition by each treatment (relative to no treatment) is shown. For the details refer to Experimental Procedures.