Active legumain is conformationally destabilized at neutral pH. pH-dependent melting curves of super-activated legumain in the presence and absence of an active site-directed inhibitor are shown. Activated legumain was incubated at the indicated pH values and thermal denaturation was measured by the Thermofluor method. An increase in fluorescence indicates the exposure of hydrophobic protein segments which accompanies protein unfolding. Melting points are indicated.