Fig 3.

Plant proteases activate human protease-activated receptors (PARs). Single-cell imaging of (a) bromelain (2 µmol L⁻¹), (b) ficin (1.5 µmol L⁻¹) and (c) papain (2.17 µmol L⁻¹) induced responses in HeLa cells transfected with either PAR2 or PAR4 as measured by ratiometric calcium imaging in cells loaded with fura-2.⁹ Labels of curves for bromelain and ficin correspond to those for papain. The responses to PAR2 and PAR4 were blocked by the protease inhibitor E64 (10 µmol L⁻¹). Other negative controls included cells transfected with either salmon sperm DNA or PAR1. Positive controls for PAR2 and PAR4 included cathepsin while thrombin served as a positive control for PAR1 and PAR4 (not shown). Proteases were added as indicated.