Fig. 4.

Caspase-3-like protease activity after incubation with proteasome inhibitors. Cultured neurons were incubated with different concentrations of Z-LLLal or 20 μm Z-LLL as indicated for 6, 12, 18, 24, 36, and 48 hr, collected, and lysed in caspase-3 buffer. The protein concentration of these lysates was determined using the Bio-Rad protein assay system. Total protein (20 μg) was incubated with 40 μm DEVD-MCA for 60 min at 37°C. Caspase-3-like protease activity was determined by measuring cleavage of the fluorogenic substrate DEVD-MCA using Hitachi fluorescence spectrophotometer and is shown as relative caspase-3-like protease activity. Caspase-3-like protease activity increased by the treatment with Z-LLLal in a dose-dependent manner. Displayed values are the means ± SD of four independent experiments. *p < 0.01, compared with DMSO group.