Comparable proteasome capacity and workload in primary PCs from AL amyloidosis and MM patients. Primary AL and MM PCs, purified as in Figure 1, were assayed in vitro for proteasome capacity (10 AL and 7 MM samples) and workload (5 AL and 6 MM samples). (A) Total cellular proteasome activity (capacity) was determined by means of an established fluorogenic peptide specifically probing the chymotryptic activity of the 20S proteolytic core (LLVY-amc), and expressed as peptide cleavage per total proteins over time. (B) Proteasome workload was estimated by automated, unbiased quantification of the intracellular accumulation of ubiquitinated proteins, upon immunofluorescent staining. Both graphs show each patient’s average value, and each group’s mean ± standard error (Student t test). MFI, mean fluorescence intensity.