Purification and characterization of recombinant catalytically active mPR3. (A) Purified recombinant mPR3 and pro-mPR3 after SDS-PAGE separation and staining with Coomassie brilliant blue; molecular mass markers are on the left. (B) Enzymatic activity of recombinant mPR3 (⋄), which was determined by measuring the increase of light absorption at 405-nm wavelength during hydrolysis of the paranitroanilide substrate MeOSuc-Ala-Ala-Pro-Val-pNA. Enzymatic activity is completely inhibited by an excess of bovine α₁-antitrypsin (▵). Pro-mPR3 does not hydrolyze the substrate (not shown). Data points represent the mean of triplicate measurements after various incubation times. Error bars indicate the SD of the mean. □ indicates data points for the buffer solution.