Endothia parasitica Protease. Parameters Affecting Stability of the Rennin-like Enzyme

Abstract

Endothia parasitica protease had maximum stability at pH 3.8 to 4.5. At 50C only 30% activity was lost after 30 minutes. At 24.1C, the enzyme was stable from pH 3.0 to 6.5 for 3 hours but was rapidly inactivated below pH 2.5 and above pH 7. The activation energy of inactivation, Ea, was 51,500 cal/mole at pH 5.5 to 6.5. Inactivation of the enzyme in this pH region resulted in decreased solubility of the protein but did not produce detectable ninhydrin-reactive groups. At pH 2.5, Ea was 14,100 cal/ mole and inactivation resulted in fragmentation of the molecule and the production of appreciable ninhydrin-reactive groups. Increase in ionic strength had a stabilizing effect on the enzyme at pH 6.5 but decreased stability of the enzyme at pH 2.5. The nature of the buffer affected stability of the enzyme (greater stability; Tris>acetate>phosphate). The effect of cations and anions on stability of the enzyme followed the order expected from previous data on the influence of ions on the general stability of proteins. Endothia parasitica protease was rapidly denatured by low concentrations of urea (2M) at pH 2.5 and 6.5, but was reasonably stable to 2M urea solutions at pH 3.5. There was no effect of 0.01M mercaptoethanol on stability of the enzyme at pH 2.5, 3.5, and 6.5.