FIGURE 3.

Progressive degradation of Fl-HPHQ₁₀RR by proteasomes. Two additional samples from the reaction that generated the spectrum in Fig. 2 were taken at 90 and 270 min of incubation and analyzed by MALDI-TOF. A, ion frequency of Fl-HPH-peptides containing 1–10 glutamine residues is plotted for samples taken at 30, 90, and 270 min and shows the progressive shortening of peptide products as the reaction proceeds. B, separate timed samples from the same reaction were analyzed by gel filtration on a 10/30 Superdex Peptide column, and the elution profiles show a similar progressive degradation of Fl-HPHQ₁₀RR to small peptides over the 270 min of incubation.