Fig. 3.

Serine proteases inhibit mucin degradation. Analysis of sputum MUC5AC and MUC5B by western blot after incubation at 37 °C over 24 h with or without of protease inhibitors. Sputum was obtained from a COPD subject 5–6 weeks after an acute exacerbation. Mucin concentration of the native control without incubation over 24 h was set to 100 %. a We used the serine protease inhibitors DFP, PMSF and TLCK, the metalloprotease inhibitors EDTA and GM6001 and the cysteine protease inhibitors leupeptin and E64. Analysis was performed in triplicate. b Incubation of COPD sputa (5–6 weeks after the onset) with A1-PI (n = 4) and compared with control sputa