FIG. 6.

Effects of temperature and pH on the activity of the M. thermophila 20S proteasome. (A) The heterologously produced 20S proteasome was assayed for PG (•) or CL (○) activity at the indicated temperatures by using (final concentrations) 250 μM Cbz-LLE-βNa and 6% (vol/vol) dimethyl sulfoxide (•) or 20 μM Suc-LLVT-Amc and 0.4% dimethyl sulfoxide (○). Specific activities are expressed as nanomoles of product per minute per milligram of protein. (B) The heterologously produced 20S proteasome was assayed for PG (•, ▪, ▴) or CL (○, □, ▵) activity at 37°C and the indicated pH by using (final concentrations) 150 μM Cbz-LLE-βNa and 6% (vol/vol) dimethyl sulfoxide (•, ▪, ▴) or 20 μM Suc-LLVY-Amc and 0.4% (vol/vol) dimethyl sulfoxide (○, □, ▵). Reaction mixtures contained the following buffers (final concentrations): 50 mM morpholineethanesulfonic acid (•, ○), 100 mM Tris-Cl (▪, □), or 50 mM ••• (▴, ▵). Specific activities are expressed as nanomoles of product per minute per milligram of protein.