3.4.22.14 additional information - thermal stability of Act d 1 and Act d 2 is strongly pH dependent. Act d 1 is irreversibly destabilized in acidic solutions (pH 3.5) 3.4.22.14 2.1 - 1-2 s, 40% of the catalytic sites survive 3.4.22.14 2.4 - 1-2 s, 75% of the catalytic sites survive 3.4.22.14 2.5 - above, 1-2 s, stable 3.4.22.14 3 12 immobilized actinidin is more stable than free form at pH 3 and pH 12 after 60 min incubation leading to 30% residual activity of immobilized form and complete inactivation of the free form