Concentration-dependent inhibition of human neutrophil cathepsin G and human neutrophil elastase activation by Bm-SPN-2. Recombinant Bm-SPN-2 at different concentrations was mixed with human neutrophil cathepsin G or human neutrophil elastase before the addition of specific substrates. Changes in the rate of substrate cleavage were used to calculate the percentage of inhibition at each Bm-SPN-2 concentration.