Calculation of the proteasome load/capacity ratio in MM cell lines.

Proteasome load = % [3H]Leu incorporated in the protein during a 1 h incubation×% of short–lived proteins broken down during first hour of the chase×inhibition by ZL3ek. Capacity = specific activity of the chymotrypsin-like sites. To calculate activity per cells chymotrypsin-like activity was measured in lysates prepared in the whole cell lysis buffer from a defined number of cells. Results for a specific activity are averages ± S.E.M of three biological replicates.Protein synthesis was measured for 1 h as described in Experimental procedures. Values are averages ± S.E.M of 2–6 independent experiments. % inhibition by ZL3ek is from Table 1.Load/capacity was calculated by dividing proteasomal degradation by specific chymotrypsin-like activity.