Table II Effect of proteasome inhibitors on the digestion of the 31-mer substrate
No InhibitorMG-132Epoxomicin
Amount digested100%28.9%54.3%
N. of digestion products802816
Peptides involving dual cleavagea66 (82.5%)20 (71.4%)7 (43.8%)
N. of cleaved peptide bondsb29 (96.7%)22 (73.3%)19 (63.3%)
N. of productive species for the A68 ligandc4 (5.1%)2 (7.1%)1 (6.3%)
Relative yield of productive cleavagesd6.9%5.5%2.6%
N. of destructive cleavages for the A68 ligande10 (34.5%)8 (36.4%)4 (21.1%)
Relative yield of the destructive cleavagesd20.3%26.3%7.8%
N. of productive species for the B27 ligandc12 (15.2%)2 (7.1%)2 (12.5%)
Relative yield of productive cleavagesd28.2%14.6%17.0%
N. of destructive cleavages for the B27 ligande9 (31%)6 (27.3%)7 (36.8%)
Relative yield of the destructive cleavagesd25.9%18.3%45.8%
Destruction/production ratio for the A68 ligandf2.94.83.0
Destruction/production ratio for the B27 ligandf0.91.32.7
  • a Percent relative to the total number of digestion products.

  • b Percent relative to the total number of peptide bonds in the substrate.

  • c Peptides with the right C-terminus and right or extended N-terminus. Percent values are relative to the total number of digestion products (see Table VS).

  • d Added values from Table VIS. For productive cleavages the yields correspond to the relative contribution of cleavage after R17 or Y25 for the A68 and B27 ligands, respectively.

  • e Cleaved peptide bonds implying destruction of the epitope. Percent values are relative to the total number of cleaved peptide bonds.

  • f Ratio between the joint relative yield of cleavages implying destruction of the natural ligand and that of the potentially productive peptides.