Fig. 5.

Inactivation and reactivation pathways of β-tryptase. Active β-tryptase tetramer converts to inactive monomers in the absence of heparin at pH 7.4, probably through an inactive tetrameric intermediate, though an active monomeric intermediate has not been excluded. Inactive β-tryptase monomers become active as monomers at low concentrations when at pH 6.0 in the presence of heparin. Active β-tryptase monomers convert to active tetramers at higher concentrations. B12 Fab mAb modulates β-tryptase activity by converting tetramers to monomers that are enzymatically active at pH 6.0, but inactive at pH 7.4.